MAINTAINERS: Add additional file to uncore frequency control

Add additional Documentation file in the list of files.
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

MAINTAINERS

@@ -9920,6 +9920,7 @@ INTEL UNCORE FREQUENCY CONTROL
 M:	Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
 L:	platform-driver-x86@vger.kernel.org
 S:	Maintained
+F:	Documentation/admin-guide/pm/intel_uncore_frequency_scaling.rst
 F:	drivers/platform/x86/intel/uncore-frequency.c
 
 INTEL VENDOR SPECIFIC EXTENDED CAPABILITIES DRIVER