update porting.md

PORTING.md

@@ -1,7 +1,13 @@
 
 ## Windows
 
-Porting to Windows shouldn't be hard when using Cygwin. Make sure to install `gcc` (because `clang` seems to work poorly on Cygwin), update the Makefile to use `gcc` and update the `CFLAGS` variable - remove `-g3` and `-fPIC`, add `-D_WIN32`. Replace `.so` with `.dll` in the shared library name.
+Crosscompiling to Windows is supported:
+
+```bash
+CC=i686-w64-mingw32-gcc make
+# or
+CC=x86_64-w64-mingw32-gcc make
+```
 
 ## M1 MacOS