Add some documentation on how to enable the lity module.

Closes #3205157

README.md

@@ -58,3 +58,10 @@ Under the "repositories" section of composer.json, add the following:
 2. Run `composer require jsor/lity` 
 
 Run `composer require drupal/lity` to install this module.
+
+
+# Enable Lity module
+
+```
+drush en lity -y && drush en lity_popup -y
+```