Document build instructions.

[Screwtapello]

Fixes #60, #379

[Achaean]

THANKS!!! :-)

I tried something like "make -C bsnes build=release install", but it failed.

>make -C bsnes build=release install
make: Entering directory '/home/giorgos/TEMPG/bsnes-115/bsnes'
Compiling ../hiro/hiro.cpp ...
Package gtksourceview-2.0 was not found in the pkg-config search path.
Perhaps you should add the directory containing `gtksourceview-2.0.pc'
to the PKG_CONFIG_PATH environment variable
Package 'gtksourceview-2.0', required by 'virtual:world', not found
In file included from ../hiro/core/core.cpp:8,
from ../hiro/hiro.cpp:5:
../hiro/core/../gtk/header.hpp:34:12: fatal error: cairo.h: No such file or directory
34 |   #include <cairo.h>
|            ^~~~~~~~~
compilation terminated.
make: *** [../hiro/GNUmakefile:73: obj/hiro-gtk2.o] Error 1
make: Leaving directory '/home/giorgos/TEMPG/bsnes-115/bsnes'
>

BTW, there's no such package at the repositories.
There is indeed libgtksourceview available, but at v.3-5. Not v.2.

[Screwtapello]

Are you building from the latest commit, b730433? We should be using GtkSourceView version 3 now.

[Achaean]

Ooops!!!
I downloaded the last stable version (from Releases page).
I didn't realize that is 6yo!

I cloned the last source code and everything went perfect!
THANKS AGAIN!!! :-)