Discourage onReadable / onWritable and recommend amphp/byte-stream instead

This also documents the stream chunk size issue mentioned in #65.

Fixes #65.

docs/event-loop/api.md

@@ -99,7 +99,7 @@ Loop::run(function () {
 
 ## Stream IO Watchers
 
-Stream watchers are how we know when we can read and write to sockets and other streams. These events are how we're able to actually *create* things like HTTP servers and asynchronous database libraries using the event loop. As such, stream IO watchers form the backbone of any useful non-blocking Amp application.
+Stream watchers are how we know when we can read and write to sockets and other streams. These events are how we're able to actually create things like HTTP servers and asynchronous database libraries using the event loop. As such, stream IO watchers form the backbone of any useful non-blocking Amp application.
 
 There are two types of IO watchers:
 
@@ -108,6 +108,9 @@ There are two types of IO watchers:
 
 ### `onReadable()`
 
+{:.note}
+> This is an advanced low-level API. Most users should use [`amphp/byte-stream`](https://github.com/amphp/byte-stream) instead.
+
 Watchers registered via `Loop::onReadable()` trigger their callbacks in the following situations:
 
  - When data is available to read on the stream under observation
@@ -144,8 +147,14 @@ In the above example we've done a few very simple things:
  - When we read data from the stream in our triggered callback we pass that to a stateful parser that does something domain-specific when certain conditions are met.
  - If the `fread()` call indicates that the socket connection is dead we clean up any resources we've allocated for the storage of this stream. This process should always include calling `Loop::cancel()` on any event loop watchers we registered in relation to the stream.
 
+{:.warning}
+> You should always read a multiple of the configured chunk size (default: 8192), otherwise your code might not work as expected with loop backends other than `stream_select()`, see [amphp/amp#65](https://github.com/amphp/amp/issues/65) for more information.
+
 ### `onWritable()`
 
+{:.note}
+> This is an advanced low-level API. Most users should use [`amphp/byte-stream`](https://github.com/amphp/byte-stream) instead.
+
  - Streams are essentially *"always"* writable. The only time they aren't is when their respective write buffers are full.
 
 A common usage pattern for reacting to writability involves initializing a writability watcher without enabling it when a client first connects to a server. Once incomplete writes occur we're then able to "unpause" the write watcher using `Loop::enable()` until data is fully sent without having to create and cancel new watcher resources on the same stream multiple times.