net/http: improve Request.Form and Request.PostForm documentation

Request.PostForm gets populated with form data for PATCH, POST, or PUT
http verbs.

Change-Id: I33065aa78a8470c4e9490aac830aa6f5963c61cb
Reviewed-on: https://go-review.googlesource.com/c/go/+/187821Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

src/net/http/request.go

@@ -237,12 +237,12 @@ type Request struct {
 	Host string
 
 	// Form contains the parsed form data, including both the URL
-	// field's query parameters and the POST or PUT form data.
+	// field's query parameters and the PATCH, POST, or PUT form data.
 	// This field is only available after ParseForm is called.
 	// The HTTP client ignores Form and uses Body instead.
 	Form url.Values
 
-	// PostForm contains the parsed form data from POST, PATCH,
+	// PostForm contains the parsed form data from PATCH, POST
 	// or PUT body parameters.
 	//
 	// This field is only available after ParseForm is called.