README: add basic instructions for enabling OE-Classic functionality

This wasn't documented anywhere so I've added it here. I'm not sure
it'll get used outside of the live OE index but it's at least useful for
anyone else who needs to debug it.

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

README

@@ -152,6 +152,54 @@ Otherwise, you can just run the plain migration command:
 python3 manage.py migrate
 
 
+Support for OE-Classic
+----------------------
+
+The Layer index optionally provides a means to index OE-Classic on a
+one-off import basis and then compare what was there to what you have
+now in the indexed layers (with some graphs showing how much of it has
+been migrated/superseded).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
+     - Bitbake branch: 1.12
+     - Enable updates: NOT enabled
+     - 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
+
+2. Clone OE-Classic somewhere locally on the machine running the
+   layer index:
+
+   git clone git://git.openembedded.org/openembedded
+
+3. Clone a bitbake somewhere locally and check out the 1.12 branch:
+
+   git clone git://git.openembedded.org/bitbake -b 1.12
+
+4. Run import_classic.py, specifying the path to OE-Classic and
+   the bitbake you checked out:
+
+   layerindex/tools/import_classic.py /path/to/bitbake112 /path/to/oeclassic
+
+5. Update the migration status of OE-Classic recipes based on other
+   layers in the database:
+
+   layerindex/tools/update_classic_status.py
+
+If you refresh the main page of the website, the OE-Classic data should
+now show up at the bottom of the branch drop-down menu. On a periodic
+basis you can repeat the last step to update the migration status in case
+new recipes are brought across (or replacements are created). Users with
+sufficient permissions can also manually update the migration status on
+the OE-Classic recipe detail pages within the website, which is useful
+for example when there's a replacement 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.
+
+
+
 Maintenance
 -----------