[workerd-cxx] added patches descriptions (#10)

Author: mikea

PATCHES.md

@@ -0,0 +1,11 @@
+Important changes:
+
+- `no-abort` replacing panic with exception handling.
+- `require lifetime annotations on all returned references` - `no-abort` dependency
+
+Misc changes:
+- `__WORKERD_CXX__ define to identify when workerd-cxx fork is in use` crate names are still
+    `cxx*`, so extra mechanism is needed to identify the presence of the fork.
+- `build fixes` to better suit our build environment. These might be obsolete since there seems to 
+    better rules_rust support upstream.
+- `site fixes` fixing CI not to build a site and to run periodically

README.md

@@ -1,3 +1,7 @@
+**This project is a fork of an excellent [cxx](https://crates.io/crates/cxx) crate for
+workerd/edgeworker projects. See [PATCHES.md](PATCHES.md) for the list of changes***
+
+
 CXX — safe FFI between Rust and C++
 =========================================