add comment for units

Author: shishirx34

src/NuGet.Server/Web.config

@@ -66,6 +66,7 @@
       </system.Web>
   -->
   <system.web>
+    <!-- maxRequestLength is specified in Kb -->
     <httpRuntime maxRequestLength="30720" />
     <compilation debug="true" targetFramework="4.6" />
   </system.web>
@@ -86,6 +87,7 @@
     </handlers>
     <security>
       <requestFiltering>
+        <!-- maxAllowedContentLength is specified in Bytes -->
         <requestLimits maxAllowedContentLength="31457280"/>
       </requestFiltering>
     </security>