Usage instructions in readme

Author: sfackler

README.md

@@ -5,6 +5,105 @@
 Syntax extensions to automatically derive `FromSql` and `ToSql` implementations for Postgres enum,
 domain, and composite types.
 
+The generated code requires rust-postgres 0.11.3 or higher and Rust 1.6.0 or higher.
+
+# Usage
+
+postgres-derive can be used both as a syntax extension with a nightly build of the compiler, or
+as a code generator with stable builds.
+
+## Nightlies
+
+Simply depend on the `postgres-derive-macros` crate and register it as a plugin:
+
+
+Cargo.toml
+```toml
+# ...
+
+[dependencies]
+postgres-derive-macros = "0.1"
+postgres = "0.11.3"
+```
+
+lib.rs
+```rust
+#![feature(plugin, custom_derive)]
+#![plugin(postgres_derive_macros)]
+
+#[macro_use]
+extern crate postgres;
+
+#[derive(Debug, ToSql, FromSql)]
+pub enum Mood {
+    Sad,
+    Ok,
+    Happy,
+}
+
+// ...
+```
+
+## Stable
+
+Use `syntex` along with `postgres-derive-codegen` in a build script:
+
+Cargo.toml
+```toml
+[package]
+# ...
+build = "build.rs"
+
+[build-dependencies]
+postgres-derive-codegen = "0.1"
+syntex = "0.29"
+
+[dependencies]
+postgres = "0.11.3"
+```
+
+build.rs
+```rust
+extern crate syntex;
+extern crate postgres_derive_codegen;
+
+use std::env;
+use std::path::Path;
+
+pub fn main() {
+    let out_dir = env::var_os("OUT_DIR").unwrap();
+    let mut registry = syntex::Registry::new();
+    postgres_derive_codegen::register(&mut registry);
+
+    let src = Path::new("src/types.rs.in");
+    let dst = Path::new(&out_dir).join("types.rs");
+
+    registry.expand("", &src, &dst).unwrap();
+}
+```
+
+types.rs.in
+```rust
+#[derive(Debug, ToSql, FromSql)]
+pub enum Mood {
+    Sad,
+    Ok,
+    Happy,
+}
+```
+
+lib.rs
+```rust
+#[macro_use]
+extern crate postgres;
+
+include!(concat!(env!("OUT_DIR"), "/types.rs"));
+
+// ...
+```
+
+# Types
+
 ## Enums
 
 Postgres enums correspond to C-like enums in Rust: