Add PATCH description

Author: Jan Jahoda

xml/System.Net.Http/HttpMethod.xml

@@ -471,8 +471,8 @@
         <ReturnType>System.Net.Http.HttpMethod</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>To be added.</summary>
-        <value>To be added.</value>
+        <summary>Represents an HTTP PATCH protocol method.</summary>
+        <value>Returns <see cref="T:System.Net.Http.HttpMethod" />.</value>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>