doc: update README.md

Author: kaspar030

README.md

@@ -2,3 +2,21 @@
 
 **git-cache-rs** is a git helper that allows caching clones in a central folder
 so consequtive clones become faster.
+
+It works by first cloning into a cache folder (`~/.gitcache` by default), then
+cloning locally out from there. The next time the same repository is cloned, it
+will be cloned from the cache.
+
+## Installation
+
+    cargo install git-cache
+
+## How to use
+
+Just use `git cache clone <clone options>` instead of `git clone <clone
+options>`. Add `-U` if you'd like the cached version to update from the
+original repository before cloning (not needed for the first clone).
+
+## License
+
+git-cache-rs is licensed under the terms of the Apache License (Version 2.0).