Move documentation from wiki to main repo

Makes it easier to keep documentation up to date and can deploy with
GitHub pages.

README.md moved to docs/README.md and is shared with GitHub Pages home
page.

docs/setup/precompiled_binaries.md

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+---
+layout: default
+title: Precompiled Binaries
+parent: Setup
+nav_order: 1
+permalink: /setup/precompiled-binaries
+---
+
+# Precompiled Binaries
+{: .no_toc }
+
+Installing GodotXterm using precompiled binaries means that you wont be required
+to use a C/C++ compiler to build the project from source. It is simply a matter
+of copying files to the correct location in your project. These files can be
+installed from several sources:
+
+1. TOC
+{:toc}
+
+**Note:** precompiled binaries will only work with certain versions of Godot
+(usually the current stable release). If you need binaries for a different or
+custom Godot version, or want to make modifications to the C/C++ code, please
+refer to the section on [Building From Source](/setup/building-from-source).
+
+## Godot Asset Library
+GodotXterm can be installed from the [Godot Asset Library](https://godotengine.org/asset-library/asset/1007).
+See the [Godot Asset Library documentation](https://docs.godotengine.org/en/stable/community/asset_library/using_assetlib.html) for more info on how to use it.
+
+## Gd-plug Plugin Manager
+If you are using the gd-plug plugin manager you can add the following line to your `plug.gd` file:
+```
+plug("lihop/godot-xterm-dist", {commit = "a1131a562e8e8f0c57b0ddf61de7fa015d463ba0", include = ["addons/godot_xterm"]})
+```
+Replace the commit hash with the hash of the GodotXterm version you wish to install.
+See [tags](https://github.com/lihop/godot-xterm-dist/tags) for a list of versions and their corresponding commit hashes.
+See the [gd-plug documentation](https://github.com/imjp94/gd-plug/blob/master/README.md) for more info on how to use it.
+
+## Manual Installation
+Alternatively, GodotXterm can be installed manually in two steps:
+1. Copy the [`addons/godot_xterm`](https://github.com/lihop/godot-xterm/tree/stable/addons/godot_xterm) directory to the `addons` directory of your Godot project.
+2. Copy the GDNative binaries into `addons/godot_xterm/native/bin` directory.
+
+The easiest way to obtain the GDNative binaries is to download them from [the Releases page](https://github.com/lihop/godot-xterm/releases).
+Download the zip archive named `libgodot-xterm-release.zip` and extract its contents into the `/addons/godot_xterm/native/bin` directory of your project.
+After this your `addons/godot_xterm/native/bin` directory should contain the following files:
+- `libgodot-xterm.javascript.32.wasm`
+- `libgodot-xterm.linux.32.so`
+- `libgodot-xterm.linux.64.so`
+- `libgodot-xterm.osx.64.dylib`
+- `libgodot-xterm.windows.32.dll`
+- `libgodot-xterm.windows.64.dll`
+
+Debug builds are also available on the Releases page if required.
+Download and unzip `libgodot-xterm-debug.zip` instead of `libgodot-xterm-release.zip` to the same location.