Added the release notes MD file and corresponding node entry in the TOC.html file

Author: DeepakRajSundar

xamarin-android/Release-Notes/v31.1.18.md

@@ -0,0 +1,16 @@
+---
+title: Essential Studio® for Xamarin.Android Release Notes  - v31.1.18
+description: Learn here about Essential Studio® for Xamarin.Android Weekly Nuget Release - Release Notes - v31.1.18
+platform: Xamarin.Android
+documentation: ug
+---
+
+# Essential Studio® for Xamarin.Android - v31.1.18 Release Notes
+
+{% include release-info.html date="September 10, 2025"  version="v31.1.18" %}
+
+{% directory path: _includes/release-notes/v31.1.18 %}
+
+{% include {{file.url}} %}
+
+{% enddirectory %}