update installation instructions

Author: furlongm

INSTALL.md

@@ -157,10 +157,13 @@ production deployments. MySQL or PostgreSQL are better choices.
 
 To configure the sqlite database backend:
 
-1. Create the database directory specified in the settings file:
+1. Create the database directory specified in the settings file, touch the
+database file and set the journal mode to WAL:
 
 ```shell
 mkdir -p /var/lib/patchman/db
+touch /var/lib/patchman/db/patchman.db
+sqlite3 /var/lib/patchman/db/patchman.db 'PRAGMA journal_mode=WAL;'
 ```
 
 2. Modify `/etc/patchman/local_settings.py` as follows: