sh: Ensure environment editor is available

When setting the environment variable EDITOR in the shell, ensure that
the editor being set is actually available: It first tries nvim, then
falls back to micro, then nano (one of which really every distribution
should have).

sh/.config/sh/env

@@ -20,7 +20,17 @@ export LIBRARYROOT="${LIBRARYROOT:-$HOME/documents/library}"
 export BIBFILE="${BIBFILE:-$LIBRARYROOT/academia/academia.bib}"
 
 # these are my personal 'important' application settings
-export EDITOR="nvim"
+if exist nvim; then
+    export EDITOR="nvim"
+elif exist vim; then
+    export EDITOR="vim"
+elif exist vi; then
+    export EDITOR="vi"
+elif exist micro; then
+    export EDITOR="micro"
+else
+    export EDITOR="nano"
+fi
 export BROWSER="qutebrowser"
 export TERMINAL="wezterm"
 export PAGER="less"