docs: document C API setup for WASIp2 and wasi:http (#12979)

Author: ShoosounS47

docs/WASI-api.md

@@ -1,7 +1,30 @@
 # WASI API
 
-Development of the WASI API has now moved to the WASI CG Subgroup; see
-the [github repository], including the [API documentation].
+Development of WASI has moved to the WASI CG Subgroup; see the
+[WASI repository] and the [interfaces page on wasi.dev].
 
-[github repository]: https://github.com/WebAssembly/WASI/
-[API documentation]: https://github.com/WebAssembly/WASI/blob/main/legacy/preview1/docs.md
+For Wasmtime embedders using the C API with the component model:
+
+* Add core WASI imports to your component linker with
+  [`wasmtime_component_linker_add_wasip2`].
+* If your component imports `wasi:http`, also add
+  [`wasmtime_component_linker_add_wasi_http`].
+* Configure store-local WASI state with [`wasmtime_context_set_wasi`], and
+  initialize WASI HTTP with [`wasmtime_context_set_wasi_http`] (after WASI).
+
+See these headers for current signatures and feature-gating details:
+
+* [`wasmtime/component/linker.h`]
+* [`wasmtime/store.h`]
+
+For legacy preview1 documentation, see the [preview1 docs].
+
+[WASI repository]: https://github.com/WebAssembly/wasi
+[interfaces page on wasi.dev]: https://wasi.dev/interfaces
+[`wasmtime_component_linker_add_wasip2`]: https://github.com/bytecodealliance/wasmtime/blob/main/crates/c-api/include/wasmtime/component/linker.h
+[`wasmtime_component_linker_add_wasi_http`]: https://github.com/bytecodealliance/wasmtime/blob/main/crates/c-api/include/wasmtime/component/linker.h
+[`wasmtime_context_set_wasi`]: https://github.com/bytecodealliance/wasmtime/blob/main/crates/c-api/include/wasmtime/store.h
+[`wasmtime_context_set_wasi_http`]: https://github.com/bytecodealliance/wasmtime/blob/main/crates/c-api/include/wasmtime/store.h
+[`wasmtime/component/linker.h`]: https://github.com/bytecodealliance/wasmtime/blob/main/crates/c-api/include/wasmtime/component/linker.h
+[`wasmtime/store.h`]: https://github.com/bytecodealliance/wasmtime/blob/main/crates/c-api/include/wasmtime/store.h
+[preview1 docs]: https://github.com/WebAssembly/WASI/blob/main/legacy/preview1/docs.md