Clarify what CE and EE means for newcomers

CONTRIBUTING.md

@@ -4,6 +4,11 @@ Thank you for your interest in contributing to GitLab.
 This guide details how contribute to GitLab in a way that is efficient for everyone.
 If you have read this guide and want to know how the GitLab core-team operates please see [the GitLab contributing process](PROCESS.md).
+GitLab comes into two flavors, GitLab Community Edition (CE) our free and open
+source edition, and GitLab Enterprise Edition (EE) which is our commercial
+edition. Throughout this guide you will see references to CE and EE for
+abbreviation.
+
 ## Contributor license agreement
 By submitting code as an individual you agree to the [individual contributor license agreement](doc/legal/individual_contributor_license_agreement.md). By submitting code as an entity you agree to the [corporate contributor license agreement](doc/legal/corporate_contributor_license_agreement.md).
@@ -227,4 +232,4 @@ This code of conduct applies both within project spaces and in public spaces whe
 Instances of abusive, harassing, or otherwise unacceptable behavior can be reported by emailing contact@gitlab.com
-This Code of Conduct is adapted from the [Contributor Covenant](http://contributor-covenant.org), version 1.1.0, available at [http://contributor-covenant.org/version/1/1/0/](http://contributor-covenant.org/version/1/1/0/)
\ No newline at end of file
+This Code of Conduct is adapted from the [Contributor Covenant](http://contributor-covenant.org), version 1.1.0, available at [http://contributor-covenant.org/version/1/1/0/](http://contributor-covenant.org/version/1/1/0/)