Document usage

README.md

@@ -3,7 +3,7 @@
 Request tracker to Zammad migration script. This is not an out of box solution
 for everybody, you will probably have to customize it.
 
-Known issues:
+## Known issues
 
 * Disabled users from RT can not be accessed by API, thus will lack email
   address and will fail to be created. Enable all users prior to the migration.
@@ -15,6 +15,17 @@ Known issues:
   * Safer approach might be to use own SMTP server and temporarily discard all
     mail from Zammad for the migration run.
 
+## Maintenance status
+
 No further development is expected there. This was used once to migrate
 [Weblate](https://weblate.org/) and I have no intent to improve this script
 myself. Pull requests are still welcome though.
+
+## Usage
+
+1. Prepare virtualenv and install dependencies: `virtualenv .venv --python python 3; . .venv/bin/activate ; pip install -r requirements.txt`
+2. Start `rt2zammad.py`, it will display template for configuration file.
+3. Fill in the template and save it as `rt2zammad.json`.
+4. Start `rt2zammad.py` to perform the migration.
+5. Verify the migration results.
+6. In case you need to roll back Zammad, please follow https://community.zammad.org/t/reset-database-to-start-from-zero/326