Flesh out the extension page

docs/extend.md

-*Extend*
+# Extend
+
+**CiviCRM Extensions** are packaged pieces of functionality that extend CiviCRM's out-of-the-box functionality, independent of CMS plaform.
+
+This section covers writing extensions, submitting extensions to the public extensions directory, and the review process for extensions submitted to the directory.
 
 TODO:
 
  * General overview: Use APIv3 and hooks. Package code in Civi extensions or CMS extensions (w/trade-offs).
  * Assimilate: http://wiki.civicrm.org/confluence/display/CRMDOC/Create+an+Extension
  * Assimilate: http://wiki.civicrm.org/confluence/display/CRMDOC/Publish+an+Extension
+ * Assimilate: https://wiki.civicrm.org/confluence/display/CRMDOC/Extension+Review
+ * Create a CiviCRM extension developer's guide to best practices (Nicolas?)
+ * Reference this page from the wiki and also https://civicrm.org/extensions (in the header).