[PATCH] Cross-compilation document

[Tim Northover]

> ================
> Comment at: docs/HowToCrossCompile.rst:73
> @@ +72,3 @@
> + * ``sub`` = for ARM: v5, v6m, v7a, v7m, etc
> + * ``sys`` = none, linux, darwin etc.
> + * ``abi`` = eabi, gnueabi, androideabi, gnueabihf, etc
> ----------------
> Wouldn't hurt to mention Windows here?

These examples generally rather ARM-centric. You don't even mention
"gnu" as an ABI, which seems to be what *everything* except 32-bit ARM
uses under Linux. "el"/"eb" is another one.

Cheers.

Tim.