Added documentation to rust_binary::out_binary (#772)

* Added documentation to `rust_binary::out_binary`

* Updated comment

* Regenerate documentation

Author: UebelAndre

docs/defs.md

@@ -226,7 +226,7 @@ Hello world
 | <a id="rust_binary-deps"></a>deps |  List of other libraries to be linked to this library target.<br><br>These can be either other <code>rust_library</code> targets or <code>cc_library</code> targets if linking a native library.   | <a href="https://bazel.build/docs/build-ref.html#labels">List of labels</a> | optional | [] |
 | <a id="rust_binary-edition"></a>edition |  The rust edition to use for this crate. Defaults to the edition specified in the rust_toolchain.   | String | optional | "" |
 | <a id="rust_binary-linker_script"></a>linker_script |  Link script to forward into linker via rustc options.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | None |
-| <a id="rust_binary-out_binary"></a>out_binary |  -   | Boolean | optional | False |
+| <a id="rust_binary-out_binary"></a>out_binary |  Force a target, regardless of it's <code>crate_type</code>, to always mark the file as executable. This attribute is only used to support wasm targets but is expected to be removed following a resolution to https://github.com/bazelbuild/rules_rust/issues/771.   | Boolean | optional | False |
 | <a id="rust_binary-proc_macro_deps"></a>proc_macro_deps |  List of <code>rust_library</code> targets with kind <code>proc-macro</code> used to help build this library target.   | <a href="https://bazel.build/docs/build-ref.html#labels">List of labels</a> | optional | [] |
 | <a id="rust_binary-rustc_env"></a>rustc_env |  Dictionary of additional <code>"key": "value"</code> environment variables to set for rustc.<br><br>rust_test()/rust_binary() rules can use $(rootpath //package:target) to pass in the location of a generated file or external tool. Cargo build scripts that wish to expand locations should use cargo_build_script()'s build_script_env argument instead, as build scripts are run in a different environment - see cargo_build_script()'s documentation for more.   | <a href="https://bazel.build/docs/skylark/lib/dict.html">Dictionary: String -> String</a> | optional | {} |
 | <a id="rust_binary-rustc_env_files"></a>rustc_env_files |  Files containing additional environment variables to set for rustc.<br><br>These files should  contain a single variable per line, of format <code>NAME=value</code>, and newlines may be included in a value by ending a line with a trailing back-slash (<code>\</code>).<br><br>The order that these files will be processed is unspecified, so multiple definitions of a particular variable are discouraged.   | <a href="https://bazel.build/docs/build-ref.html#labels">List of labels</a> | optional | [] |

docs/flatten.md

@@ -317,7 +317,7 @@ Hello world
 | <a id="rust_binary-deps"></a>deps |  List of other libraries to be linked to this library target.<br><br>These can be either other <code>rust_library</code> targets or <code>cc_library</code> targets if linking a native library.   | <a href="https://bazel.build/docs/build-ref.html#labels">List of labels</a> | optional | [] |
 | <a id="rust_binary-edition"></a>edition |  The rust edition to use for this crate. Defaults to the edition specified in the rust_toolchain.   | String | optional | "" |
 | <a id="rust_binary-linker_script"></a>linker_script |  Link script to forward into linker via rustc options.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | None |
-| <a id="rust_binary-out_binary"></a>out_binary |  -   | Boolean | optional | False |
+| <a id="rust_binary-out_binary"></a>out_binary |  Force a target, regardless of it's <code>crate_type</code>, to always mark the file as executable. This attribute is only used to support wasm targets but is expected to be removed following a resolution to https://github.com/bazelbuild/rules_rust/issues/771.   | Boolean | optional | False |
 | <a id="rust_binary-proc_macro_deps"></a>proc_macro_deps |  List of <code>rust_library</code> targets with kind <code>proc-macro</code> used to help build this library target.   | <a href="https://bazel.build/docs/build-ref.html#labels">List of labels</a> | optional | [] |
 | <a id="rust_binary-rustc_env"></a>rustc_env |  Dictionary of additional <code>"key": "value"</code> environment variables to set for rustc.<br><br>rust_test()/rust_binary() rules can use $(rootpath //package:target) to pass in the location of a generated file or external tool. Cargo build scripts that wish to expand locations should use cargo_build_script()'s build_script_env argument instead, as build scripts are run in a different environment - see cargo_build_script()'s documentation for more.   | <a href="https://bazel.build/docs/skylark/lib/dict.html">Dictionary: String -> String</a> | optional | {} |
 | <a id="rust_binary-rustc_env_files"></a>rustc_env_files |  Files containing additional environment variables to set for rustc.<br><br>These files should  contain a single variable per line, of format <code>NAME=value</code>, and newlines may be included in a value by ending a line with a trailing back-slash (<code>\</code>).<br><br>The order that these files will be processed is unspecified, so multiple definitions of a particular variable are discouraged.   | <a href="https://bazel.build/docs/build-ref.html#labels">List of labels</a> | optional | [] |

rust/private/rust.bzl

@@ -860,7 +860,14 @@ _rust_binary_attrs = {
         cfg = "exec",
         allow_single_file = True,
     ),
-    "out_binary": attr.bool(),
+    "out_binary": attr.bool(
+        doc = (
+            "Force a target, regardless of it's `crate_type`, to always mark the " +
+            "file as executable. This attribute is only used to support wasm targets but is " +
+            "expected to be removed following a resolution to https://github.com/bazelbuild/rules_rust/issues/771."
+        ),
+        default = False,
+    ),
 }
 
 rust_binary = rule(