Document PERMISSION table handling in v4 migration guide

Signed-off-by: nscuro <nscuro@protonmail.com>

Author: nscuro

docs/guides/administration/migrating-from-v4.md

@@ -145,8 +145,8 @@ v4-migrator bootstrap \
   --target-pass
 ```
 
-After this, the target has the v5 schema but no rows.
-The migrator's later phases populate `PERMISSION`, `LICENSE`, `TEAM`, etc. directly from your v4 source.
+After this, the target has the v5 schema and a seeded `PERMISSION` catalog (the well-known set of v5 permissions).
+No other rows are written by bootstrap; the migrator's later phases populate `LICENSE`, `TEAM`, `USER`, and the rest from your v4 source.
 
 ### 2. Verify the target
 
@@ -505,6 +505,8 @@ v4-migrator bootstrap --target-url ... --target-user ... --target-pass
 v4-migrator load      --target-url ... --target-user ... --target-pass
 ```
 
+`bootstrap` re-seeds the v5 `PERMISSION` catalog after applying the schema, so the rerun of `load` can resolve permission foreign keys without re-running `transform`.
+
 !!! warning
 
     Don't manually `TRUNCATE` individual v5 tables and re-run `load`.