docs(proxy-wasm) document response body buffering behavior

docs/PROXY_WASM.md

@@ -383,6 +383,7 @@ specifications and different SDK libraries:
 - [Tested SDKs](#tested-sdks)
 - [Supported Entrypoints](#supported-entrypoints)
 - [Supported Host ABI](#supported-host-abi)
+- [Supported Properties](#supported-properties)
 
 [Back to TOC](#table-of-contents)
 
@@ -578,7 +579,7 @@ implementation state in ngx_wasm_module:
 -------------------------------------------:|:------------------:|:-------------------:|:----------------
 *Request properties*                        |                    |
 `request.path`                              | :heavy_check_mark: | :x:                 | Maps to [ngx.request_uri](https://nginx.org/en/docs/http/ngx_http_core_module.html#var_request_uri).
-`request.url_path`                          | :heavy_check_mark: | :x:                 | Maps to [ngx.uri](https://nginx.org/en/docs/http/ngx_http_core_module.html#uri). 
+`request.url_path`                          | :heavy_check_mark: | :x:                 | Maps to [ngx.uri](https://nginx.org/en/docs/http/ngx_http_core_module.html#uri).
 `request.host`                              | :heavy_check_mark: | :x:                 | Maps to [ngx.hostname](https://nginx.org/en/docs/http/ngx_http_core_module.html#hostname).
 `request.scheme`                            | :heavy_check_mark: | :x:                 | Maps to [ngx.scheme](https://nginx.org/en/docs/http/ngx_http_core_module.html#scheme).
 `request.method`                            | :heavy_check_mark: | :x:                 | Maps to [ngx.request_method](https://nginx.org/en/docs/http/ngx_http_core_module.html#request_method).
@@ -671,12 +672,13 @@ factors are at play when porting the SDK to a new Host proxy runtime.
 
 Proxy-Wasm's design was primarily influenced by Envoy concepts and features, but
 because Envoy and Nginx differ in underlying implementations there remains a few
-limitations on some supported features:
+limitations on some supported features (non-exhaustive list):
 
 1. Pausing a filter (i.e. `Action::Pause`) can only be done in the following
    steps:
     - `on_http_request_headers`
     - `on_http_request_body`
+    - `on_http_response_body` (to enable body buffering)
     - `on_http_call_response`
 
 2. The "queue" shared memory implementation does not implement an automatic