Add pipeline status and coverage status images. Add a bit more of information.

README.md

-# purism-username-policy
+# Purism's username polivy for wordpress
 
-This is a Wordpress plugin that implements rules for usernames of the liberty platform.
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+[![pipeline status](https://source.puri.sm/liberty/ldh_wp_username_policy/badges/master/pipeline.svg)](https://source.puri.sm/liberty/ldh_wp_username_policy/commits/master)
+[![coverage report](https://source.puri.sm/liberty/ldh_wp_username_policy/badges/master/coverage.svg)](https://source.puri.sm/liberty/ldh_wp_username_policy/commits/master)
+
+This is a Wordpress plugin that implements rules for usernames of the liberty platform. These rules are as follows:
+
+* Remove all characters after the first "@"
+* Remove all remaining non-alphanumeric characters
+* If username starts with a numeral, prepend an "x"
+* Set all letters to lowercase
+* Other Wordpress logic should apply (e.g. avoid duplicates by adding a number)