Merge pull request #15 from schmengler/doc-ThisInTemplate

Add documentation for ThisInTemplateSniff

Author: lenaorobei

Magento/Sniffs/Templates/ThisInTemplateSniff.md

@@ -0,0 +1,13 @@
+# Rule: Do not use `$this` in templates
+## Background
+In PHTML templates, the current block is available as `$this` and `$block`. The alternative with `$this` has been deprecated and should not be used anymore.
+
+## Reasoning
+`$this` in templates is a legacy from Magento 1. It still works, however this can change any time, should templates and blocks be further decoupled. That's why for new code you should always use `$block` and restrict it to public methods.
+
+## How it works
+Any occurence of `$this` in PHTML files (via file pattern in ruleset.xml) raises a warning. 
+
+## How to fix
+
+Replace `$this` with `$block`. If you use private or protected methods, make them public.