Bug 1893159 - add technical docs for phabricator to fx-source-docs, r=bgrins

Differential Revision: https://phabricator.services.mozilla.com/D208487

docs/contributing/data-review.rst

@@ -0,0 +1,41 @@
+Data Review
+-----------
+
+**Everything that lands in mozilla-central that adds or expands data
+collection must go through the data review process.**
+
+This will require assessing the sensitivity of the data that is being
+collected, and going through the `sensitive data collection
+process <https://wiki.mozilla.org/Data_Collection#Step_3:_Sensitive_Data_Collection_Review_Process>`__
+if necessary. All data collection is subject to our `overall data
+collection policy <https://wiki.mozilla.org/Data_Collection>`__.
+
+Documentation for the data collection request process and the
+expectations we have for people following it `lives on the
+wiki <https://wiki.mozilla.org/Data_Collection#Requesting_Data_Collection>`__.
+This document describes the technical implementation in Phabricator
+using tags.
+
+1. Any change that touches metrics will be automatically flagged with a
+   ``needs-data-classification`` tag by Phabricator, using `this herald
+   rule <https://phabricator.services.mozilla.com/H436>`__. If a change
+   adds/updates data collection in a way that doesn’t automatically
+   trigger this rule, this tag should be added manually (and if
+   appropriate, please file a bug to update the herald rule so it
+   happens automatically next time).
+
+2. After assessing data sensitivity, the tag can be replaced with either
+   ``data-classification-low`` or ``data-classification-high`` depending
+   on that sensitivity.
+
+3. Adding ``data-classification-high`` will auto-add the ``#data-stewards``
+   reviewer group as a blocking reviewer for the change and initiate the
+   `sensitive data review process <https://wiki.mozilla.org/Data_Collection#Step_3:_Sensitive_Data_Collection_Review_Process>`__.
+
+4. For patches making mechanical changes that happen to trigger the
+   herald rule linked above, but that do not actually add or update any
+   data collection, the ``data-classification-unnecessary`` tag can be used.
+
+Patches with the ``needs-data-classification`` tag will not be landable in
+Lando. The process linked above must be followed in order to land the
+change.

docs/contributing/index.rst

@@ -15,6 +15,7 @@ development process and source code documentation.
    reviews
    levelling-up
    how_to_submit_a_patch
+   data-review
 
 
 .. toctree::