Add some minimal documentation about method support

Author: micgro42

README.md

@@ -7,6 +7,12 @@ in the [Wikibase Lexeme extension](https://www.mediawiki.org/wiki/Extension:Wiki
 It intentionally covers only a subset of Vue Template syntax that is used by the Wikibase
 Lexeme extension. It is not going to cover all elements of Vue Template language.
 
+## Migration notes
+
+For the purpose of migrating to Vue 3, very basic support for the method syntax was added as an alternative to filters.
+In order to keep the interface stable, method callbacks should also be provided as the third parameter when calling
+`Templating::render()`.
+
 ## Installation
 
 The recommended way of installing the library is using [Composer](https://getcomposer.org),

src/FilterExpressionParsing/FilterCall.php

@@ -2,6 +2,9 @@
 
 namespace WMDE\VueJsTemplating\FilterExpressionParsing;
 
+/**
+ * This represents both calls to a filter and calls to a method.
+ */
 class FilterCall {
 
 	/**