docs(install): add how to install helix from snap (#7625)

book/src/install.md

@@ -9,6 +9,7 @@ # Installing Helix
   - [Arch Linux extra](#arch-linux-extra)
   - [NixOS](#nixos)
   - [Flatpak](#flatpak)
+  - [Snap](#snap)
   - [AppImage](#appimage)
 - [macOS](#macos)
   - [Homebrew Core](#homebrew-core)
@@ -104,6 +105,23 @@ ### Flatpak
 flatpak run com.helix_editor.Helix
 ```
 
+### Snap
+
+Helix is available on [Snapcraft](https://snapcraft.io/helix) and can be installed with:
+
+```sh
+snap install --classic helix
+```
+
+This will install Helix as `/snap/bin/helix` (so make sure `/snap/bin` is in your `PATH`), which is not the preferred invocation (`hx`).
+As a workaround you can manually alias the command globally with:
+
+```sh
+snap alias helix hx
+```
+
+Or, otherwise, just alias in your shell's config.
+
 ### AppImage
 
 Install Helix using the Linux [AppImage](https://appimage.org/) format.