Add info on updating re rpm and source installs rockstor#319

contribute/contribute.rst

@@ -288,6 +288,25 @@ Be sure to check that the resulting build behaves as expected over:
 In (1.) above a db wipe is initiated helping to test the self-start code capability.
 See the initrock script and it's systemd trigger service: rockstor-init.
 
+A note on updating
+``````````````````
+A source install will consider any rpm version to be an update.
+And this 'update' will necessarily delete all prior settings / db setup.
+This is by design as a source release is intended only for development.
+Identifying itself as *ROCKSTOR UNKNOWN VERSION* withing the top-right of the Web-UI.
+For example if work on say a hardware compatibility issue is submitted,
+upon that work being merged and released in the next rpm version the author can 'update' in-place.
+There-by returning the specific hardware instance to a recognised upgrade path.
+Providing also for a double-check on if the released rpm, fix included, works as intended.
+The source install can, in-turn, now simply be removed via :code:`rm -rf /opt/rockstor-dev/`.
+Rpm installs live exclusively in /opt/rockstor, bar their associated systemd units.
+
+All :ref:`import_data` and :ref:`config_backup` functionality is supported similarly;
+as there is no source difference between a source and rpm install, just the packaging/update/support service.
+Unless of course there has been a breaking change involved in the submitted code.
+Breaking changes in these areas are strongly discouraged but unavoidable at time.
+An example: one cannot restore a new features settings to an older Rockstor instance.
+
 Change -> Test cycle
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