Create CPU_MAX_USAGE.md

doc/CPU_MAX_USAGE.md

@@ -0,0 +1,26 @@
+# Maximum CPU usage
+
+Please read this document carefully, `max-threads-hint` (was known as `max-cpu-usage`) option is most confusing option in the miner with many myth and legends.
+This option is just hint for automatic configuration and can't precise define CPU usage.
+
+### Option definition
+#### Config file:
+```json
+{
+    ...
+    "cpu": {
+        "max-threads-hint": 100,
+        ...
+    },
+    ...
+}
+```
+
+#### Command line
+`--cpu-max-threads-hint 100`
+
+### Known issues and usage
+
+* This option has no effect if miner already generated CPU configuration, to prevent config generation use `"autosave":false,`.
+* Only threads count can be changed, for 1 core CPU this option has no effect, for 2 core CPU only 2 values possible 50% and 100%, for 4 cores: 25%, 50%, 75%, 100%. etc. 
+* You CPU may limited by other factors, eg cache.