added docs for git pr

Author: beardyman

README.md

@@ -13,6 +13,7 @@ git finish
 git rename
 git promote
 git open
+git pr
 ```
 
 ## Installation
@@ -104,6 +105,11 @@ cd my-git-repo
 git open
 ```
 
+Open a pull request for your current branch
+```shell
+git pr
+```
+
 Start a new branch
 ```shell script
 git start feature myBranch