update readme with help and usage

Author: softprops

README.md

@@ -1,3 +1,34 @@
 # git-codeowners [![Build Status](https://travis-ci.org/softprops/git-codeowners.svg?branch=master)](https://travis-ci.org/softprops/git-codeowners)
 
+# usage
+
+git-codeowners is intended for use as a git extention ( a program whose name starts with git- ) to extend your git workflow.
+
+```bash
+$ git codeowners src/main.rs
+@softprops
+```
+
+```bash
+$ git-codeowners --help
+git-codeowners 0.1.0
+Github CODEOWNERS answer sheet
+
+USAGE:
+    git-codeowners [FLAGS] [OPTIONS] <path>
+
+FLAGS:
+    -e, --emails     Only return emails
+    -h, --help       Prints help information
+    -t, --teams      Only return teams
+    -u, --users      Only return users
+    -V, --version    Prints version information
+
+OPTIONS:
+    -c, --codeowners <codeowners>    An explicit path for a CODEOWNERS file. program will exit 1 if file can not be resolved
+
+ARGS:
+    <path>    Path of file in git repo. if '-' is provided path will be read from stdin. program will exit 2 if no owners can be resolved
+```
+
 Doug Tangren (softprops) 2017