add migration documentation for aerleon

Author: loulecrivain

docs/admin/upgrade.md

@@ -9,3 +9,16 @@ As part of the upgrade for Nautobot 2.0 it is recommended to perform a stepped u
 ## Upgrade Guide
 
 When a new release comes out it may be necessary to run a migration of the database to account for any changes in the data models used by this app. Execute the command `nautobot-server post-upgrade` within the runtime environment of your Nautobot installation after updating the `nautobot-firewall-models` package via `pip`.
+
+## Migrating from Capirca to Aerleon
+
+Previous versions of nautobot-firewall-app used Capirca as their backend for firewall configuration generation.
+Please make sure to follow the steps below while migrating from a version of this app which used Capirca
+as a backend (latest is v2.2.2) to the newest version with Aerleon:
+
+* Reinstall dependencies.
+* Migrate your `nautobot_config.py`. Configuration keys with `capirca_` prefix have been renamed to `aerleon_`.
+* Run database migrations as usual.
+
+There are no breaking changes between Capirca and Aerleon generators. Normally you should not have to change any
+firewall rules and/or policies.