Add postgresql

.gitignore

 *.retry
+vendor

README.md

+# Install Ansible dependencies
+```
+ansible-galaxy install -r dependencies.yml -p vendor
+```

coopdevs.yml

@@ -7,3 +7,4 @@
     - common
     - http-server
     - coopdevs.org
+    - role: vendor/geerlingguy.postgresql

dependencies.yml

+- src: geerlingguy.postgresql
+  version: 1.3.1