Update README.

Author: rwjblue

README.md

@@ -1,3 +1,21 @@
 ## git-repo-info
 
-Retrieves repo information.
+Retrieves repo information without relying on the `git` command.
+
+### Usage
+
+```javascript
+var getRepoInfo = require('git-repo-info');
+
+var info = getRepoInfo();
+
+info.branch         //=> will be the current branch
+info.sha            //=> will be the current sha
+info.abbreviatedSha //=> will be the first 10 chars of the current sha
+```
+
+When called without any arguments, `git-repo-info` will automatically lookup upwards
+into parent directories to find the first match with a `.git` folder.
+
+If passed an argument, it will be assumed to be the path to the repo's `.git` folder
+to inspect.