converted INSTALL to Markdown

moved licensing information to the README

INSTALL.md

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+To run OpenRA, several files are needed from the original game disks.
+A minimal asset pack can also be downloaded and installed by the game.
+
+The following lists per-platform dependencies required to build from source.
+
+Windows
+=======
+
+* [.NET Framework >= 4.0 (Client Profile)](http://www.microsoft.com/en-us/download/details.aspx?id=17113)
+* [Cg Toolkit >= 2.2 (optional, for Cg renderer)](https://developer.nvidia.com/cg-toolkit-download)
+* [SDL 1.2 (included)](http://libsdl.org/download-1.2.php)
+* [SDL 2 (optional)](http://www.libsdl.org/download-2.0.php)
+* [FreeType (included)](http://gnuwin32.sourceforge.net/packages/freetype.htm)
+* [zlib (included)](http://gnuwin32.sourceforge.net/packages/zlib.htm)
+* [OpenAL (included)](http://kcat.strangesoft.net/openal.html)
+
+To compile OpenRA, open the `OpenRA.sln` solution in the main folder,
+or build it from the command-line with MSBuild.
+
+Copy both the native DLLs from `.\packaging\windows`
+and the CLI images from `.\thirdparty` to the main folder.
+
+Run the game with `OpenRA.Game.exe Game.Mod=ra` for Red Alert
+or `OpenRA.Game.exe Game.Mod=cnc` for Tiberian Dawn.
+
+Linux
+=====
+
+To grab the bundled CLI DLLs type `make dependencies`.
+To compile OpenRA, run `make all` from the command line.
+Run with either `launch-game.sh' or `mono --debug OpenRA.Game.exe'.
+
+Type 'sudo make install-all' for system wide installation. You
+can then run from the `openra` shortcut.
+
+Debian/Ubuntu
+-------------
+
+* mono-dmcs
+* libmono-winforms2.0-cil
+* cli-common-dev (>= 2.10)
+* freetype
+* openal
+* sdl
+* nvidia-cg-toolkit (optional, for Cg renderer)
+
+Slackware
+---------
+
+The following packages from slackbuilds.org are required, on 13.37 32-bit:
+* libgdiplus
+* mono
+* openAL
+* nvidia-cg-toolkit (optional, for Cg renderer)
+
+openSUSE
+--------
+
+* mono-devel
+* openal
+* freetype2
+* SDL
+* cg (optional, for Cg renderer)
+
+Gentoo
+------
+
+* dev-lang/mono
+* dev-dotnet/libgdiplus
+* media-libs/openal
+* media-gfx/nvidia-cg-toolkit (optional, for Cg renderer)