Update README badges

Author: minad

README.org

@@ -1,6 +1,8 @@
 #+TITLE: Gnuplot for Emacs
 
 #+html: <a href="https://www.gnu.org/software/emacs/"><img alt="GNU Emacs" src="https://github.com/minad/corfu/blob/screenshots/emacs.svg?raw=true"/></a>
+#+html: <a href="https://elpa.nongnu.org/nongnu/gnuplot.html"><img alt="NonGNU ELPA" src="https://elpa.nongnu.org/nongnu/gnuplot.svg"/></a>
+#+html: <a href="https://elpa.nongnu.org/nongnu-devel/gnuplot.html"><img alt="NonGNU-devel ELPA" src="https://elpa.nongnu.org/nongnu-devel/gnuplot.svg"/></a>
 #+html: <a href="https://melpa.org/#/gnuplot"><img alt="MELPA" src="https://melpa.org/packages/gnuplot-badge.svg"/></a>
 #+html: <a href="https://stable.melpa.org/#/gnuplot"><img alt="MELPA Stable" src="https://stable.melpa.org/packages/gnuplot-badge.svg"/></a>
 
@@ -18,8 +20,9 @@ above.
 
 * Installation
 
-The easiest way to install =gnuplot= is to directly get it from [[https://melpa.org][MELPA]]. After
-configuring Emacs to use MELPA, you should be able to install =gnuplot= by typing
+The easiest way to install =gnuplot= is to directly get it from [[https://elpa.nongnu.org/][ELPA]] or [[https://melpa.org][MELPA]].
+After configuring Emacs to use MELPA, you should be able to install =gnuplot= by
+typing
 
 : M-x install-package RET gnuplot RET