Add 'POSTINSTALL.md'

POSTINSTALL.md

@@ -0,0 +1,11 @@
+# Essential Packages
+
+```bash
+apt install git zsh
+```
+
+# Setup SSH 
+
+```
+ssh-keygen -o -a 100 -t ed25519 -f ~/.ssh/id_ed25519 -C "johnnie@posteo.de"
+```