Add capture/release for results in package:async

pkg/async/README.md

Index: pkg/async/README.md
diff --git a/pkg/async/README.md b/pkg/async/README.md
index dc34553bf8a2ac69fde5c5f3cc96bd4b9bbf8ee7..73a40f4418e2a0fc42ab6dacad8c07d8ac8388e4 100644
--- a/pkg/async/README.md
+++ b/pkg/async/README.md
@@ -4,8 +4,16 @@ The package contains sub-libraries with different utilities.
 
 ### Zipping streams
 
-The "stream_zip.dart" sub-library contains functionality to combine several streams
-of events into a single stream of tuples of events.
+The "stream_zip.dart" sub-library contains functionality
+to combine several streams of events into a single stream of tuples of events.
+
+### Results
+The "result.dart" sub-library introduces a `Result` class that can hold either
+a value or an error.
+It allows capturing an asynchronous computation which can give either a value
+or an error, into an asynchronous computation that always gives a `Result`
+value, where errors can be treated as data.
+It also allows releasing the `Result` back into an asynchronous computation.
 
 ### History.
 This package is unrelated to the discontinued `async` package with version 0.1.7.