integrate ETW windows event tracing into mimalloc as another track tool

src/prim/windows/readme.md

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+## Primitives:
+
+- `prim.c` contains Windows primitives for OS allocation.
+
+## Event Tracing for Windows (ETW)
+
+- `etw.h` is generated from `etw.man` which contains the manifest for mimalloc events.
+  (100 is an allocation, 101 is for a free)
+
+- `mimalloc.wprp` is a profile for the Windows Performance Recorder (WPR).
+  In an admin prompt, you can use:
+  ```
+  > wpr -start src\prim\windows\mimalloc.wprp -filemode
+  > <my mimalloc program>
+  > wpr -stop test.etl
+  ``` 
+  and then open `test.etl` in the Windows Performance Analyzer (WPA).