Adjust documents

Author: taiki-e

futures-async-macro/README.md

@@ -7,7 +7,7 @@ Add this to your `Cargo.toml`:
 
 ```toml
 [dependencies]
-futures-preview = { version = "0.3.0-alpha.14", features = ["async-stream", "nightly"] }
+futures-preview = { version = "0.3.0-alpha.15", features = ["async-stream", "nightly"] }
 ```
 
 ### \#\[for_await\]
@@ -17,6 +17,7 @@ Processes streams using a for loop.
 This is a reimplement of [futures-await]'s `#[async]` for loops for futures 0.3 and is an experimental implementation of [the idea listed as the next step of async/await](https://github.com/rust-lang/rfcs/blob/master/text/2394-async_await.md#for-await-and-processing-streams).
 
 ```rust
+#![feature(async_await, generators, stmt_expr_attributes, proc_macro_hygiene)]
 use futures::for_await;
 use futures::prelude::*;
 
@@ -26,13 +27,16 @@ for value in stream::iter(1..=5) {
 }
 ```
 
-`value` has the `Item` type of the stream passed in. Note that async for loops can only be used inside of `async` functions or `#[async_stream]` functions.
+`value` has the `Item` type of the stream passed in. Note that async for loops can only be used inside of `async` functions, closures, blocks, `#[async_stream]` functions and `async_stream_block!` macros.
 
 ### \#\[async_stream\]
 
+Creates streams via generators.
+
 This is a reimplement of [futures-await]'s `#[async_stream]` for futures 0.3 and is an experimental implementation of [the idea listed as the next step of async/await](https://github.com/rust-lang/rfcs/blob/master/text/2394-async_await.md#generators-and-streams).
 
 ```rust
+#![feature(async_await, generators)]
 use futures::prelude::*;
 use futures::async_stream;
 

futures-async-macro/src/lib.rs

@@ -19,6 +19,7 @@ mod error;
 
 mod elision;
 
+/// Processes streams using a for loop.
 #[proc_macro_attribute]
 pub fn for_await(args: TokenStream, input: TokenStream) -> TokenStream {
     assert_!(args.is_empty(), args_is_not_empty!("for_await"));
@@ -28,6 +29,7 @@ pub fn for_await(args: TokenStream, input: TokenStream) -> TokenStream {
     Expand(Future).fold_expr(Expr::ForLoop(expr)).into_token_stream().into()
 }
 
+/// Creates streams via generators.
 #[proc_macro_attribute]
 pub fn async_stream(args: TokenStream, input: TokenStream) -> TokenStream {
     assert_!(args.is_empty(), args_is_not_empty!("async_stream"));
@@ -180,6 +182,7 @@ fn expand_async_stream_fn(item: ItemFn) -> TokenStream {
     })
 }
 
+/// Creates streams via generators.
 #[proc_macro]
 pub fn async_stream_block(input: TokenStream) -> TokenStream {
     let input = TokenStream::from(TokenTree::Group(Group::new(Delimiter::Brace, input)));