Document Owned Files tab in the Change screen's owners UI

The owners plugin UI has a new tab displaying the list of files
owned by the current user.

Document the UI behaviour and meaning, including the limitation
of its inaccuracy in case of having owners.expandGroups = false.

Change-Id: I88a676da97fc1f009b6c7ed4bc7e385ab7cfebbc
diff --git a/owners/src/main/resources/Documentation/how-to-use.md b/owners/src/main/resources/Documentation/how-to-use.md
index 148fd97..4a4d17f 100644
--- a/owners/src/main/resources/Documentation/how-to-use.md
+++ b/owners/src/main/resources/Documentation/how-to-use.md
@@ -122,3 +122,28 @@
 
 The owners status per file in replacement mode doesn't differ from
 [submit requirements mode](#ownersStatus.submitRequirement.files).
+
+### Files that are assigned to the current user based on the OWNERS
+
+When the current user is mentioned directly or indirectly via a group
+ownership as the owner of one or more files, the change screen displays
+an additional tab called _Owned Files_.
+
+![owned_files](./owned-files.png "Owned Files")
+
+The tab indicates whether the current user has review duties  based on the
+icon displayed on the right side of the tab. If the icon is an orange
+clock, the current user is required to review the files indicated in the
+tab; otherwise, if the icon is a green tick, then the current user review
+input is not strictly required for the change to be merged.
+
+The list of files included in the _Owned Files_ tab, a subset of the full
+list displayed in the _Files_ tab, are the ones assigned to the
+current user through the OWNERS file.
+
+> **NOTE**: When the `owners.config` has `owners.expandGroups = false`
+> then the association between files and the current user may not be
+> accurate or not available because of the lack of group expansion and
+> account resolution service on the backend. In this case, the
+> _Owned Files_ tab may be absent even if the current user is effectively
+> owner of one or more files in the change.
diff --git a/owners/src/main/resources/Documentation/owned-files.png b/owners/src/main/resources/Documentation/owned-files.png
new file mode 100644
index 0000000..f88cbee
--- /dev/null
+++ b/owners/src/main/resources/Documentation/owned-files.png
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