Add contributing guidelines

doc/CONTRIBUTING.md

@@ -0,0 +1,51 @@
+Guidelines for contributing to LibreNMS
+---------------------------------------
+
+- Don't submit code whose license conflicts with the GPLv3.  If you're not
+  sure, consult the [Free Software Foundation's license list][1] and see if
+  your code's license is on the compatible or incompatible list.
+  - The SNMP MIBs may be moved to a separate repository soon due to this
+    issue.  We will do everything we can to ensure this has minimal impact.
+  - The current Observium license is incompatible with GPLv3.  Do not submit
+    patches from current Observium unless you are the copyright holder, and
+    specifically note that you are releasing it under GPLv3.
+
+- Test your patches first.  It's easy to set up git to push to a bare
+  repository on a local test system, and pull from this into your live
+  installation at very frequent intervals.
+
+- Don't break the poller.  User interface blemishes are not critical, but
+  losing data from network monitoring systems might be.
+
+- Please join us in IRC at irc.freenode.net in channel ##librenms if you're
+  able.  Collaborating in real time makes the coordination of contributions
+  easier.
+
+
+Proposed workflow for submitting pull requests (currently untested)
+-------------------------------------------------------------------
+
+This is a proposed workflow designed to minimise the scope of merge
+conflicts when submitting pull requests:
+- Fork the [LibreNMS repo master branch][2] in your own GitHub account.
+- Create an [issue][3] explaining what work you plan to do.
+- Create a branch in your copy of the repo called issue-###, where ### is
+  the issue number you created.
+- Make and test your changes in the issue branch as needed - this might take
+  a few days or weeks.
+- When you are happy with your issue branch's changes and ready to submit
+  your patch, update your copy of the master branch to the current revision;
+  this should just result in a fast forward of your copy of master.
+- Rebase your issue branch from your clone of master.  Fix any conflicts at
+  this stage.
+- Merge your issue branch back into of your copy of master. Again, this
+  should be a simple fast forward.
+- Submit a pull request for your patch from your copy of master.
+
+[1]: http://www.gnu.org/licenses/license-list.html
+"Free Software Foundation's license list"
+[2]: https://github.com/librenms/librenms/tree/master
+"LibreNMS master branch"
+[3]: https://github.com/librenms/librenms/issues
+"LibreNMS issue database"
+