Improve documentation on var-naming (#3042)

src/ansiblelint/rules/var_naming.md

@@ -2,10 +2,21 @@
 
 This rule checks variable names to ensure they conform with requirements.
 
-Variable names must contain only lowercase alphanumeric characters and the underscore `_` character.
-Variable names must also start with either an alphabetic or underscore `_` character.
+Variable names must contain only lowercase alphanumeric characters and the
+underscore `_` character. Variable names must also start with either an
+alphabetic or underscore `_` character.
 
-For more information see the [creating valid variable names](https://docs.ansible.com/ansible/latest/playbook_guide/playbooks_variables.html#creating-valid-variable-names) topic in Ansible documentation.
+For more information see the [creating valid variable names][var-names] topic in
+Ansible documentation and [Naming things (Good Practices for Ansible)][cop].
+
+## Settings
+
+This rule behavior can be changed by altering the below settings:
+
+```yaml
+# .ansible-lint
+var_naming_pattern: "^[a-z_][a-z0-9_]*$"
+```
 
 ## Problematic Code
 
@@ -30,3 +41,7 @@ For more information see the [creating valid variable names](https://docs.ansibl
     no_caps: bar # <- Does not contains uppercase characters.
     variable: baz # <- Does not contain special characters.
 ```
+
+[cop]: https://redhat-cop.github.io/automation-good-practices/#_naming_things
+[var-names]:
+  https://docs.ansible.com/ansible/latest/playbook_guide/playbooks_variables.html#creating-valid-variable-names