Provide links to info about ZFS Buildbot options

Add links for information about the ZFS buildbot options
to the contributing guidelines and PR template.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Closes #6235

.github/CONTRIBUTING.md

@@ -136,6 +136,8 @@ Buildbot](http://build.zfsonlinux.org/) builders before
 being accepted. If you are experiencing intermittent TEST
 builder failures, you may be experiencing a [test suite
 issue](https://github.com/zfsonlinux/zfs/issues?q=is%3Aissue+is%3Aopen+label%3A%22Test+Suite%22).
+There are also various [buildbot options](https://github.com/zfsonlinux/zfs/wiki/Buildbot-Options)
+to control how changes are tested.
 * All proposed changes must be approved by a ZFS on Linux organization member.
 
 ### Testing

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,5 +1,10 @@
 <!--- Provide a general summary of your changes in the Title above -->
 
+<!---
+Documentation on ZFS Buildbot options can be found at
+https://github.com/zfsonlinux/zfs/wiki/Buildbot-Options
+-->
+
 ### Description
 <!--- Describe your changes in detail -->
 
@@ -20,6 +25,7 @@
 - [ ] Performance enhancement (non-breaking change which improves efficiency)
 - [ ] Code cleanup (non-breaking change which makes code smaller or more readable)
 - [ ] Breaking change (fix or feature that would cause existing functionality to change)
+- [ ] Documentation (a change to man pages or other documentation)
 
 ### Checklist:
 <!--- Go over all the following points, and put an `x` in all the boxes that apply. -->