readme: Document the new implicit pdb output file naming

Author: mstorsjo

README.md

@@ -102,7 +102,10 @@ changes:
 - Add `-gcodeview` to the compilation commands (e.g. in
   `wrappers/clang-target-wrapper.sh`), together with using `-g` as usual to
   enable debug info in general.
-- Add `-Wl,-pdb,module.pdb` to linking commands.
+- Add `-Wl,-pdb=` to linking commands. This creates a PDB file at the same
+  location as the output EXE/DLL, but with a PDB extension. (By passing
+  `-Wl,-pdb=module.pdb` or `-Wl,-pdb,module.pdb` one can explicitly specify
+  the name of the output PDB file.)
 
 Even though LLVM supports this, there are a few caveats with using it when
 building in MinGW mode: