Update DllImportResolver.xml

Author: gfoidl

xml/System.Runtime.InteropServices/DllImportResolver.xml

@@ -39,7 +39,7 @@
 
 The runtime does not do any lifetime management around the handle returned by a <xref:System.Runtime.InteropServices.DllImportResolver>. It is left to the implementation and consuming code to keep the library loaded for as long as necessary and free it if/when desired. 
 
-The resolver delegate is called everytime when a PInvoke call is done. It is fine to cache the handle, as long as the consuming code does not call <xref:System.Runtime.InteropServices.NativeLibrary.Free>.
+For each entry point the resolver is called the first time PInvoke is done. As long as the library is not unloaded via <xref:System.Runtime.InteropServices.NativeLibrary.Free> it is safe to have a cache for libraryname to handle mapping.
 
       ]]></format>
     </remarks>