Include configuration warning

README.md

@@ -13,6 +13,25 @@
 
 A [PlantUML](http://plantuml.sourceforge.net/) major mode for Emacs.
 
+# Quick Guide
+
+Install with
+
+	M-x package-install<RET>
+	plantuml-mode<RET>
+
+Preview diagrams with `C-c C-c` (`plantuml-preview`).
+
+**WARNING:** This may send information to
+`"https://www.plantuml.com/plantuml"`! Check that `plantuml-jar-path`
+is correct for your use case and that `plantuml-default-exec-mode` is
+set to `jar` before previewing any sensitive material.  See [Execution modes](# Execution modes) for more information.
+
+```lisp
+	(setq plantuml-jar-path "/path/to/your/copy/of/plantuml.jar")
+	(setq plantuml-default-exec-mode 'jar)
+```
+
 # Installation
 
 Make sure you have [MELPA](http://melpa.org/) enabled in your ``emacs.d``. Then, you can just