[c] Add documentation for the C binding generator (#1319)

* Add documentation for the C binding generator

* Clarify meaning of various files

* Clarify deallocation

* Typos and formatting

* Clarify imported function cleanup

* Fix typo

* Formatting

* Code formatting

* Add free information for options, results, variants

* Code formatting, strengthen wording

* Address feedback

Author: TartanLlama

README.md

@@ -263,6 +263,8 @@ which in this case, as expected, is the same as the input world.
 
 ### Guest: C/C++
 
+See the [`wit-bindgen` C and C++ Bindings Generator documentation](/crates/c/README.md) for details.
+
 C and C++ code can be compiled for the `wasm32-wasip1` target using the [WASI
 SDK] project. The releases on that repository have precompiled `clang` binaries
 which are pre-configured to compile for WebAssembly.