Automatic port of System.Threading.ExecutionContext.Restore doc (dotnet#4887)

* Automatic port of System.Threading.ExecutionContext.Restore doc

* Update xml/System.Threading/ExecutionContext.xml

Co-authored-by: Prashanth Govindarajan <[email protected]>

* Apply suggestions from code review

Co-authored-by: carlossanlop <[email protected]>
Co-authored-by: Prashanth Govindarajan <[email protected]>

Author: 2 people

xml/System.Threading/ExecutionContext.xml

@@ -359,9 +359,17 @@
         <Parameter Name="executionContext" Type="System.Threading.ExecutionContext" Index="0" FrameworkAlternate="net-5.0" />
       </Parameters>
       <Docs>
-        <param name="executionContext">To be added.</param>
-        <summary>To be added.</summary>
-        <remarks>To be added.</remarks>
+        <param name="executionContext">The ExecutionContext to set.</param>
+        <summary>Restores a captured execution context on to the current thread.</summary>
+        <remarks>
+          <format type="text/markdown"><![CDATA[
+
+## Remarks
+
+To revert to the current execution context; capture it before calling Restore, and then call Restore it again.
+
+          ]]></format>
+        </remarks>
       </Docs>
     </Member>
     <Member MemberName="RestoreFlow">