Added benchmark and stress test

Easy to use and zero configuration embedded benchmark/stress test.

doc/BENCHMARK.md

@@ -0,0 +1,29 @@
+# Embedded benchmark
+
+You can run with XMRig with the following commands:
+```
+xmrig --bench=1M
+xmrig --bench=10M
+xmrig --bench=1M -a rx/wow
+xmrig --bench=10M -a rx/wow
+```
+This will run 1 or 10 millions RandomX hashes and print the time it took. First two commands use Monero variant (2 MB per thread, best for Zen2/Zen3 CPUs), second two commands use Wownero variant (1 MB per thread, useful for Intel and 1st gen Zen/Zen+ CPUs).
+
+Checksum of all the hashes will be also printed to check stability of your hardware: if it's green then it's correct, if it's red then there was hardware error during computation. No Internet connection is required for the benchmark.
+
+Double check that you see `Huge pages 100%` both for dataset and for all threads, and also check for `msr register values ... has been set successfully` - without this result will be far from the best. Running as administrator is required for MSR and huge pages to be set up properly.
+
+![Benchmark example](https://i.imgur.com/PST3BYc.png)
+
+### Benchmark with custom config
+
+You can run benchmark with any configuration you want. Just start without command line parameteres, use regular config.json and add `"benchmark":"1M",` on the next line after pool url. 
+
+# Stress test
+
+You can also run continuous stress-test that is as close to the real RandomX mining as possible and doesn't require any configuration:
+```
+xmrig --stress
+xmrig --stress -a rx/wow
+```
+This will require Internet connection and will run indefinitely.