➕ Add installation instructions

manual/src/SUMMARY.md

@@ -4,7 +4,7 @@
 
 # Getting Started
 
-- [Installation]()
+- [Installation](./installation.md)
 - [Hello World]()
 - [Configuration](./configuration.md)
 

manual/src/installation.md

@@ -0,0 +1,26 @@
+# Installation
+
+## Quick Installation (Unix only)
+
+Enter the command below to quickly install Allay.
+
+```console
+curl https://allay-mc.github.io/getallay/getallay.sh -sSf | sh
+```
+
+## Manual Installation
+
+Visit the [release page](https://github.com/allay-mc/allay/releases/) and
+select the archive that matches your platform. Extract it and put the
+executable to some path of your choise (usually something like `/usr/local/bin`
+on Unix and `C:\Program Files` on Windows).
+
+If your platform is not supported or you just prefer to build Allay yourself,
+then you can do so by following the instructions below.
+
+1. Make sure you have [Rust and Cargo][Rust] installed.
+2. Install with `cargo install --git https://github.com/allay-mc/allay.git` or
+   clone the repository with `git clone https://github.com/allay-mc/allay.git`
+   and then run `cargo install --path allay`.
+
+[Rust]: https://www.rust-lang.org/