Update and rename CONTRIBUTING to CONTRIBUTING.md (#594)

diff --git a/CONTRIBUTING b/CONTRIBUTING.md
similarity index 90%
rename from CONTRIBUTING
rename to CONTRIBUTING.md
index 488366b..2dda126 100644
--- a/CONTRIBUTING
+++ b/CONTRIBUTING.md
@@ -1,3 +1,4 @@
+# Contributing
 Want to contribute? Great! First, read this page (including the small print at the end).
 
 ### Before you contribute
@@ -23,5 +24,4 @@
 ### The small print
 Contributions made by corporations are covered by a different agreement than
 the one above, the
-[Software Grant and Corporate Contributor License Agreement]
-(https://cla.developers.google.com/about/google-corporate).
\ No newline at end of file
+[Software Grant and Corporate Contributor License Agreement](https://cla.developers.google.com/about/google-corporate).