Minor update to testing docs

Author: Greg Turner

docs/contributing/testing.md

@@ -32,8 +32,18 @@ test database and restores from `test_initial_data.sql` if available,
 
 This reuses the test databases, and skips collectstatic and compress steps.
 
-To achieve permanent speedip, create a data dump called `test_initial_data.sql`
+### To create a data dump with migrations applied
+
+To achieve permanent speedup, create a data dump called `test_initial_data.sql`
 with migrations applied. It will be restored to the test database in
 `runtests.sh`, bypassing all migrations.
 
+1. Create a fresh database `foo`
+2. Run migrations:
+
+        manage.py migrate
+
+3. Dump the database to `test_initial_data.sql`
+
+        `pg_dump -O -x -f test_initial_data.sql -d foo`