DOCS/crosscompile-mingw: update

- Adds description of and uses $JOBS envvar in MXE instructions
- Adds MXE_TARGETS to command line instead of echoing it to settings.mk
- Prettify and sentence usage

DOCS/crosscompile-mingw.md

@@ -6,16 +6,22 @@ produce both 32 bit and 64 bit executables. MinGW-w64 is available from
 http://mingw-w64.sourceforge.net.
 
 You have to run mpv's configure with these arguments:
-    DEST_OS=win32 TARGET=i686-w64-mingw32 ./waf configure
 
-Using mingw-w64-cmake to setup a MinGW-w64 environment is recommended (this will
-also build mpv and its dependencies): https://github.com/lachs0r/mingw-w64-cmake
+```bash
+DEST_OS=win32 TARGET=i686-w64-mingw32 ./waf configure
+```
 
-Alternatively, use MXE: http://mxe.cc
-With MXE, you have to modify the file settings.mk to target MinGW-w64 (even if
-you compile to 32 bit).
+While building a complete MinGW-w64 toolchain yourself is possible, people have
+created scripts to help ease the process. These are the two recommended methods:
 
-Warning: the original MinGW (http://www.mingw.org) is unsupported.
+- Using [mingw-w64-cmake](lachs0r/mingw-w64-cmake) to setup a MinGW-w64
+  environment. We recommend you to try this first before MXE. mingw-w64-cmake
+  will also build mpv and its dependencies.
+- Alternatively, you can use MXE: http://mxe.cc. With MXE, you have to manually
+  set the target to MinGW-w64 (even if you compile to 32 bit). A working example
+  below.
+
+**Warning**: the original MinGW (http://www.mingw.org) is unsupported.
 
 Note that MinGW environments included in Linux distributions are often broken,
 outdated and useless, and usually don't use MinGW-w64.
@@ -31,22 +37,24 @@ cd /opt
 git clone https://github.com/mxe/mxe mingw
 cd mingw
 
-# Edit the MXE target, so that MinGW-w64 for 32 bit targets is built.
-
-echo "MXE_TARGETS := i686-w64-mingw32" > settings.mk
-
 # Build required packages. The following provide a minimum required to build
-# mpv. (Not all of the following packages are strictly required.)
+# mpv.
 
-make gcc
-make ffmpeg
-make libass
-make jpeg
-make pthreads
+# The JOBS environment variable controls threads to use when building. DO NOT
+# use the regular `make -j4` option with MXE. Alternatively, you can make this
+# a default so you don't need to type `JOBS=4` every time you build:
+# echo "JOBS := 4" >> settings.mk
+
+# The MXE_TARGET environment variable builds MinGW-w64 for 32 bit targets.
+# You can make this a default:
+# echo "MXE_TARGETS := i686-w64-mingw32" >> settings.mk
+
+make gcc ffmpeg libass jpeg pthreads MXE_TARGETS=i686-w64-mingw32 JOBS=4
 
 # Build mpv. The target will be used to automatically select the name of the
 # build tools involved (e.g. it will use i686-w64-mingw32-gcc).
 
+cd ..
 git clone https://github.com/mpv-player/mpv.git
 cd mpv
 export PATH=/opt/mingw/usr/bin/:$PATH