Update README

Author: minad

README.org

@@ -29,9 +29,16 @@ The easiest way to install =gnuplot= is to directly get it from [[https://elpa.n
 or do =M-x list-packages= and search for =gnuplot= in the list. Note that there is a
 different [[https://github.com/mkmcc/gnuplot-mode][gnuplot-mode]] package on MELPA which is less featureful.
 
+* Configuration
+
+In order to customize Gnuplot, use =M-x gnuplot-customize= or set the respective
+customizable variables in your user configuration.
+
 It is recommended to configure =read-extended-command-predicate= in your Emacs
 configuration, such that =M-x= only completes commands which are relevant to the
 current mode, such that =gnuplot-*= commands are only shown in Gnuplot buffers.
+Alternatively press the key =M-X= instead of =M-x= if you want relevant commands
+only.
 
 #+begin_src emacs-lisp
 (setq read-extended-command-predicate #'command-completion-default-include-p)