Update README to mention cgroups support (#4884)

The README file for the Diagnostic Resource Monitoring library has been updated. It has been mentioned that this library uses control groups (cgroups) in Linux to monitor system resources. A note has also been added stating that it currently supports cgroups v1, but there is no support for cgroups v2.

Co-authored-by: Martin Obratil <maobrati@microsoft.com>

src/Libraries/Microsoft.Extensions.Diagnostics.ResourceMonitoring/README.md

@@ -1,6 +1,9 @@
 # Microsoft.Extensions.Diagnostics.ResourceMonitoring
 
-Measures and reports processor and memory usage.
+Measures and reports processor and memory usage. This library utilizes control groups (cgroups) in Linux to monitor system resources.
+
+> [!NOTE]
+> Currently, it supports cgroups v1 but does not have support for cgroups v2.
 
 ## Install the package