README: add setup info for other distro comparisons

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>

README

@@ -220,9 +220,10 @@ been migrated/superseded). If you want to enable this, do the following:
 
 1. From the admin interface, create a Branch record with the following
    values:
-     - Name: oe-classic
+     - Name: oe-classic (must be exactly this!)
      - Bitbake branch: 1.12
-     - Enable updates: NOT enabled
+     - Enable updates: NOT ticked
+     - Comparison: ticked
      - Update environment: if you have set up Python environments (for
        python2 vs python3 across different branches) then you'll need
        to select the python2 environment that you created here
@@ -257,6 +258,81 @@ doesn't have the same name, so the update_classic_status.py script
 wouldn't be able to pick it up.
 
 
+Setting up other distro comparisons
+-----------------------------------
+
+The Layer Index also provides optional functionality to enable comparison
+with other distributions (currently RPM-based only) in a similar manner to
+OE-Classic comparison documented above. To set this up you need to perform
+the following steps:
+
+1. From the admin interface, set up the appropriate entries:
+
+   1.1. Create a Branch with the following values:
+        - Bitbake branch: <any dummy value>
+        - Enable updates: NOT enabled
+        - Comparison: enabled
+
+   1.2. Create a Layer. Typically this would have the same name as
+        the branch although that is not a requirement. The "Comparison"
+        checkbox should be ticked. If the packages are in separate
+        repositories (one per package, as is typical in RPM-based
+        distributions such as Fedora) then in order to make the links
+        through to files work correctly you may need to use repository web
+        interface URLs similar to these:
+
+        Repository web interface tree base URL:
+          https://github.com/organisationname/%pathelement[0]%/tree/master/%pathelement[1:]%
+        Repository web interface file base URL:
+          https://github.com/organisationname/%pathelement[0]%/blob/master/%pathelement[1:]%
+
+   1.3. Create a LayerBranch to link the Branch and Layer that you
+        created in the previous steps. You don't need to enter anything
+        special here.
+
+2. Run the import script, specifying the branch and layer names and the path
+   to the base of the packages (where each subdirectory contains a package,
+   notably a spec file describing the package):
+
+   layerindex/tools/import_otherdistro.py import-pkgspec <branchname> <layername> <pkgpath>
+
+3. Update the comparison status of recipes based on layers in the database:
+
+   layerindex/tools/update_classic_status.py -l <layername> -b <branchname>
+
+4. Optionally enable the Update button in the UI by setting COMPARISON_UPDATE
+   in settings.py to map each other distro branch to the command that should
+   be run in the background when the button is pressed. For example:
+
+COMPARISON_UPDATE = [
+    {
+        'branch_name': 'otherlinux',
+        'update_command': 'layerindex/tools/import_otherdistro.py import-pkgspec otherlinux otherlinux /path/to/pkgs -u %update%; layerindex/tools/update_classic_status.py -b otherlinux -l otherlinux -u %update%',
+    },
+]
+
+If you refresh the main page of the website, the other distro data should
+now show up at the bottom of the branch drop-down menu. On a periodic
+basis you can repeat steps 2 and 3 to refresh the data as changes occur on
+both sides. Users with sufficient permissions can also manually update the
+migration status on the other distro recipe detail pages within the website,
+which is useful for example when there's an equivalent recipe in another
+layer that doesn't have the same name, so the update_classic_status.py
+script wouldn't be able to pick it up.
+
+If you want to show links to additional upstream pages associated with
+packages in the other distro, you can add "Layer recipe extra URL" entries
+for each type of link you want to be shown. For example, Fedora provides
+a summary page for each package - acl's one is at
+https://apps.fedoraproject.org/packages/acl, so you would create a
+Layer Recipe Extra URL entry with the template URL
+"https://apps.fedoraproject.org/packages/%pn%" and then links would be
+shown for this under the detail page for each package in the other distro.
+If you have the rrs application enabled the link will also be shown in the
+"Distros" section of the maintenance detail page for the covering recipe.
+
+
+
 
 Maintenance
 -----------
@@ -289,7 +365,7 @@ Bundled nv.d3.js is redistributed under the Apache License 2.0.
 
 Bundled d3.js is redistributed under the BSD License.
 
-All other content is copyright (C) 2013-2016 Intel Corporation and
+All other content is copyright (C) 2013-2018 Intel Corporation and
 licensed under the MIT license (unless otherwise noted) - see
 COPYING.MIT for details.