Shorter example external script

examples/external.sh

@@ -1,29 +1,13 @@
 #!/bin/sh
 #
 # Dummy example external script that loads/saves
-# account_key/key/cert/chain to /tmp/foo; Usage: `simp_le -f
-# external.sh`.
-
-load () {
-  cat /tmp/foo || true
-}
-
-save () {
-  cat - > /tmp/foo
-}
-
-persisted () {
-  echo account_key key cert chain
-}
+# account_key/key/cert/chain to /tmp/foo. Experiment e.g. by running
+# `./external.sh persisted`, `echo foo | ./external.sh save; cat
+# /tmp/foo`, or `./external.sh load`; note the exit codes. The plugin
+# can be loaded by running `simp_le -f external.sh`.
 
 case $1 in
-  save)
-    save
-    ;;
-  load)
-    load
-    ;;
-  persisted)
-    persisted
-    ;;
+  save) cat - > /tmp/foo;;
+  load) [ ! -f /tmp/foo ] || cat /tmp/foo;;
+  persisted) echo account_key key cert chain;;
 esac