fix: [vps] provide an informative message upon missing ``kal-shlib``

bin/vps

@@ -1,7 +1,24 @@
 #!/bin/bash
 
 
-. /etc/shlib
+. /etc/shlib >/dev/null 2>&1 || {
+    echo "Error: you don't have kal-shlib-core installed."
+    echo ""
+    echo "  You might want to add `deb.kalysto.org` deb repository, you'll need root access,"
+    echo "  so you might want to run these command after a \`sudo -i\` for instance..."
+    echo ""
+    echo "     echo deb https://deb.kalysto.org no-dist kal-alpha kal-beta kal-main \\"
+    echo "          > /etc/apt/sources.list.d/kalysto.org.list"
+    echo "     wget -O - https://deb.kalysto.org/conf/public-key.gpg | apt-key add -"
+    echo "     apt-get update -o Dir::Etc::sourcelist=sources.list.d/kalysto.org.list \\"
+    echo "         -o Dir::Etc::sourceparts=- -o APT::Get::List-Cleanup=0"
+    echo ""
+    echo "  Then install package kal-shlib-*:"
+    echo ""
+    echo "    apt install kal-shlib-{common,cmdline,config,cache,docker,pretty}"
+    echo ""
+    exit 1
+} >&2
 
 include common
 include parse