Add Snap installation instructions to guide (#253)

Author: joaopalet

INSTALLATION.md

@@ -2,7 +2,7 @@
 
 ## Package managers
 
-[![Packaging status](https://repology.org/badge/vertical-allrepos/stackit-cli.svg?columns=3)](https://repology.org/project/stackit-cli/versions)
+[![Packaging status](https://repology.org/badge/vertical-allrepos/stackit-cli.svg?columns=1)](https://repology.org/project/stackit-cli/versions)
 
 ### macOS
 
@@ -22,6 +22,16 @@ brew install stackit
 
 ### Linux
 
+#### Snapcraft
+
+The STACKIT CLI is available as a [Snap](https://snapcraft.io/stackit), and can be installed via:
+
+```shell
+sudo snap install stackit --beta --classic
+```
+
+or via the [Snap Store](https://snapcraft.io/snap-store) for desktop.
+
 #### Debian/Ubuntu (`APT`)
 
 The STACKIT CLI can be installed through the [`APT`](https://ubuntu.com/server/docs/package-management) package manager.