[doc] Restore README.mingw.md

It got deleted in cf1fdf1632 but it is
still useful. Needs to be updated to meson world, though.

README.mingw.md

@@ -0,0 +1,58 @@
+For the development of HarfBuzz, the Microsoft shaping technology, Uniscribe,
+as a widely used and tested shaper is used as more-or-less OpenType reference
+implementation and that specially is important where OpenType specification
+is or wasn't that clear. For having access to Uniscribe on Linux/macOS these
+steps are recommended:
+
+You want to follow the 32bit instructions. The 64bit equivalents are included
+for reference.
+
+1. Install Wine.
+   - Fedora: `dnf install wine`.
+
+2. Install `mingw-w64` compiler.
+   - Fedora, 32bit: `dnf install mingw32-gcc-c++`
+   - Fedora, 64bit: `dnf install mingw64-gcc-c++`
+   - Debian: `apt install g++-mingw-w64`
+   - Mac: `brew install mingw-w64`
+
+3. If you have drank the `meson` koolaid, look at `.ci/build-win32.sh` to see how to
+   invoke `meson` now, or just run that script.  Otherwise, here's how to use the
+   old trusty autotools instead:
+
+   a) Install dependencies.
+      - Fedora, 32bit: `dnf install mingw32-glib2 mingw32-cairo mingw32-freetype`
+      - Fedora, 64bit: `dnf install mingw64-glib2 mingw64-cairo mingw64-freetype`
+
+   b) Configure:
+     - `NOCONFIGURE=1 ./autogen.sh && mkdir winbuild && cd winbuild`
+     - 32bit: `../mingw-configure.sh i686`
+     - 64bit: `../mingw-configure.sh x86_64`
+
+   c) Build as usual:
+     - make
+
+   d) Configure your wine to find system mingw libraries. See:
+      https://fedoraproject.org/wiki/MinGW/Configure_wine
+
+Now you can use `hb-shape` by `(cd win32build/util && wine hb-shape.exe)`
+but if you like to shape with the Microsoft Uniscribe:
+
+4. Bring a 32bit version of `usp10.dll` for yourself from `C:\Windows\SysWOW64\usp10.dll` of your
+   Windows installation (assuming you have a 64-bit installation, otherwise
+   `C:\Windows\System32\usp10.dll`) that it is not a DirectWrite proxy
+   ([for more info](https://en.wikipedia.org/wiki/Uniscribe)).
+   Rule of thumb, your `usp10.dll` should have a size more than 500kb, otherwise
+   it is designed to work with DirectWrite which Wine can't work with its original one.
+   You want a Uniscribe from Windows 7 or older.
+
+   Put the DLL in the folder you are going to run the next command,
+
+5. `WINEDLLOVERRIDES="usp10=n" wine hb-shape.exe fontname.ttf -u 0061,0062,0063 --shaper=uniscribe`
+
+(`0061,0062,0063` means `abc`, use test/shaping/hb-unicode-decode to generate ones you need)
+
+When you have built that, you can test HarfBuzz's native shaper against Uniscribe
+following these instructions:
+
+  https://github.com/harfbuzz/harfbuzz/issues/3671