CONTRIBUTING.md: file for advice on github

CONTRIBUTING.md

@@ -0,0 +1,27 @@
+How to contribute to curl
+=========================
+
+Join the community
+------------------
+
+ 1. Click 'watch' on the github repo
+
+ 2. Subscribe to the suitable [mailing lists](http://curl.haxx.se/mail/)
+
+Read [docs/CONTRIBUTE](docs/CONTRIBUTE)
+---------------------------------------
+
+Send your suggestions using one of these methods:
+-------------------------------------------------
+
+ 1. in a mail to the mailing list
+
+ 2. in the [bug tracker](https://sourceforge.net/p/curl/bugs/)
+
+ 3. as a pull request on github
+
+ 4. as an issue on github
+   
+
+/ The cURL team!
+