selftests/resctrl: Add README for resctrl tests

resctrl tests will be implemented. README is added for the tool first.
Co-developed-by: Babu Moger <babu.moger@amd.com>
Signed-off-by: Babu Moger <babu.moger@amd.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/resctrl/README

+resctrl_tests - resctrl file system test suit
+
+Authors:
+	Fenghua Yu <fenghua.yu@intel.com>
+	Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>,
+
+resctrl_tests tests various resctrl functionalities and interfaces including
+both software and hardware.
+
+Currently it supports Memory Bandwidth Monitoring test and Memory Bandwidth
+Allocation test on Intel RDT hardware. More tests will be added in the future.
+And the test suit can be extended to cover AMD QoS and ARM MPAM hardware
+as well.
+
+BUILD
+-----
+
+Run "make" to build executable file "resctrl_tests".
+
+RUN
+---
+
+To use resctrl_tests, root or sudoer privileges are required. This is because
+the test needs to mount resctrl file system and change contents in the file
+system.
+
+Executing the test without any parameter will run all supported tests:
+
+	sudo ./resctrl_tests
+
+OVERVIEW OF EXECUTION
+---------------------
+
+A test case has four stages:
+
+  - setup: mount resctrl file system, create group, setup schemata, move test
+    process pids to tasks, start benchmark.
+  - execute: let benchmark run
+  - verify: get resctrl data and verify the data with another source, e.g.
+    perf event.
+  - teardown: umount resctrl and clear temporary files.
+
+ARGUMENTS
+---------
+
+Parameter '-h' shows usage information.
+
+usage: resctrl_tests [-h] [-b "benchmark_cmd [options]"] [-t test list] [-n no_of_bits]
+        -b benchmark_cmd [options]: run specified benchmark for MBM, MBA and CQM default benchmark is builtin fill_buf
+        -t test list: run tests specified in the test list, e.g. -t mbm, mba, cqm, cat
+        -n no_of_bits: run cache tests using specified no of bits in cache bit mask
+        -p cpu_no: specify CPU number to run the test. 1 is default
+        -h: help