chore: reword the 0install installation hint

Point directly at the download page instead of describing the
per-operating-system instructions.

Author: bastianeicher

apps/site/snippets/en/download/zeroinstall.bash

@@ -1,5 +1,4 @@
-# 0install has specific installation instructions for each operating system.
-# Please refer to the official documentation at https://get.0install.net/.
+# For instructions how to get 0install, please see https://get.0install.net/.
 
 # Add Node.js and NPM to PATH:
 0install add node https://apps.0install.net/javascript/node.xml${props.os === 'WIN' ? '' : ' --version=' + props.release.version}