API Reference method page template - add description (#36185)

* API Reference method page template - add description

* Update files/en-us/mdn/writing_guidelines/page_structures/page_types/api_method_subpage_template/index.md

Co-authored-by: Onkar Khadangale <87750369+OnkarRuikar@users.noreply.github.com>

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Co-authored-by: Onkar Khadangale <87750369+OnkarRuikar@users.noreply.github.com>

files/en-us/mdn/writing_guidelines/page_structures/page_types/api_method_subpage_template/index.md

@@ -129,6 +129,11 @@ Here is an example where a method can raise a `DOMException` with a name of `Ind
 - {{jsxref("TypeError")}}
   - : Thrown …
 
+## Description
+
+_Detailed description of how the method behaves_
+_Section omitted if an introductory paragraph (or two) at the top of the page is sufficient._
+
 ## Examples
 
 Note that we use the plural "Examples" even if the page only contains one example.