Add README for apt_dist_upgrade role

roles/apt_dist_upgrade/README.md

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+# apt_dist_upgrade
+
+Shows the packages to be upgraded and perform a dist upgrade.
+
+## Role variables
+
+* `apt_dist_upgrade_become` - Default: true. Enable/disable the Ansible become
+  functionality.
+* `apt_dist_upgrade_become_user` - Default: root. When using become functionality for
+  privilege escalation, this is the user with desired privileges you become.
+
+## Example playbook
+
+```yaml
+- hosts: my-server
+  roles:
+    - eriol.kit.apt_dist_upgrade
+```