Add compiling guide;

guides/Compiling.md

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+Compiling LÖVR
+===
+
+Compiling the LÖVR code yourself lets you create a custom LÖVR build so you can add your own
+features or run it on other operating systems.  Below is a guide for setting up all the dependencies
+and compiling the code on various types of systems.
+
+Dependencies
+---
+
+LÖVR depends on the following libraries.  They are included as submodules in the `deps` directory of
+the repository, so make sure you clone with the `--recursive` flag or run `git submodule update
+--init` in an existing repository.
+
+- Lua or LuaJIT
+- GLFW (3.2+)
+- OpenGL (3.3, ES3, or WebGL 2)
+- assimp (4+)
+- OpenVR (1.0.9, for `lovr.headset`)
+- PhysicsFS (3+)
+- OpenAL (1.17+ recommended for HRTF support)
+- FreeType
+- msdfgen
+- ODE (for `lovr.physics`)
+- Emscripten (optional, for compiling for web)
+
+Windows
+---
+
+From the `lovr` folder, run these commands to create a build folder and compile the project using
+CMake:
+
+```sh
+mkdir build
+cd build
+cmake ..
+cmake --build .
+```
+
+The executable will then exist at `/path/to/lovr/build/Debug/lovr.exe`.  A LÖVR project (a folder
+containing a `main.lua` script) can then be dropped onto `lovr.exe` to run it, or it can be run
+via the command line as `lovr.exe path/to/project`.
+
+macOS
+---
+
+Install the dependencies using your package manager of choice:
+
+```sh
+brew install assimp glfw3 luajit physfs freetype openal-soft ode libccd
+```
+
+Next, build using CMake, as above:
+
+```sh
+mkdir build
+cd build
+cmake ..
+cmake --build .
+```
+
+The `lovr` executable should exist in `lovr/build` now.  It's recommended to set up an alias or
+symlink so that this executable can be found in your PATH environment variable.  Once that's done,
+you can run a project like this:
+
+```sh
+lovr /path/to/myGame
+```
+
+> You may need to set the `PKG_CONFIG_PATH` environment variable for OpenAL to be located properly.
+> If you run into this, see [Troubleshooting](#troubleshooting) below for more info.
+
+Linux
+---
+
+First, install the dependencies using your package manager of choice.
+
+#### Arch Linux
+
+```sh
+pacman -S assimp glfw-x11 luajit physfs freetype2 openal ode
+```
+
+#### Debian/Ubuntu
+
+```sh
+sudo apt-get install build-essential cmake libassimp-dev libglfw3-dev libluajit-5.1-dev libphysfs-dev libfreetype6-dev libopenal-dev libode-dev
+```
+
+Then, build with CMake:
+
+```sh
+mkdir build
+cd build
+cmake ..
+cmake --build .
+```
+
+On Linux, LÖVR needs to run within the Steam Runtime.  To do this, first [install
+Steam](https://wiki.archlinux.org/index.php/Steam#Installation).  Next, [install the Steam udev
+rules](https://github.com/ValveSoftware/SteamVR-for-Linux#usb-device-requirements).  Then, run LÖVR
+within the Steam runtime:
+
+```sh
+~/.steam/steam/ubuntu12_32/steam-runtime/run.sh lovr
+```
+
+If you receive errors related to `libstdc++`, set the `LD_PRELOAD` environment variable when running
+the command:
+
+```sh
+LD_PRELOAD='/usr/$LIB/libstdc++.so.6 /usr/$LIB/libgcc_s.so.1' ~/.steam/steam/ubuntu12_32/steam-runtime/run.sh lovr
+```
+
+WebVR
+---
+
+First, install the Emscripten SDK.
+
+Unix:
+
+```sh
+mkdir build
+cd build
+emcmake cmake ..
+emmake make -j2
+```
+
+Windows (from a Visual Studio Command Prompt, make sure the Emscripten SDK is on PATH):
+
+```sh
+mkdir build
+cd build
+emcmake cmake -G "NMake Makefiles" ..
+emmake nmake
+```
+
+The above commands will output `lovr.js` and `lovr.wasm`.  To package a game, run:
+
+```
+python /path/to/emscripten/tools/file_packager.py game.data --no-heap-copy --preload /path/to/game@/ --js-output=game.js
+```
+
+Which will output `game.js` and `game.data`.  You can then include `lovr.js` and `game.js` on an
+HTML page with a canvas element.  Check out [`lovr-webvr-server`](https://github.com/bjornbytes/lovr-webvr-server/blob/master/views/index.ejs) for an example.
+
+Troubleshooting
+---
+
+- If you get "CMake no CMAKE_CXX_COMPILER found" on Windows, then install Visual Studio and create a
+  blank C++ project, which will prompt you to install the compilers and tools necessary to compile
+  LÖVR.
+- On macOS, if you run into an error message about not being able to find OpenAL, make sure you've
+  added the proper OpenAL directory (usually something like
+  `/usr/local/opt/openal-soft/lib/pkgconfig`) to your `PKG_CONFIG_PATH` environment variable.
+  Installing openal-soft with brew will print out a message telling you how to do this.