Add badge for MELPA stable

Didn't see the full function name since I'm using the nameless
package, blindly copied what I saw.

README.org

@@ -3,6 +3,7 @@
 
 #+begin_export html
 <a href="https://melpa.org/#/persist-state"><img alt="MELPA" src="https://melpa.org/packages/persist-state-badge.svg"/></a>
+<a href="https://stable.melpa.org/#/persist-state"><img alt="MELPA Stable" src="https://stable.melpa.org/packages/persist-state-badge.svg"/></a>
 #+end_export
 
 * Introduction
@@ -35,6 +36,7 @@ persist-state supports a number of packages out of the box. For some packages th
 - [[https://github.com/radian-software/prescient.el][Prescient.el]]
 - recentf
 - savehist
+- saveplace
 
 * Installation and usage
 

persist-state.el

@@ -102,6 +102,11 @@
   (when (bound-and-true-p savehist-mode)
     (savehist-autosave)))
 
+(defun persist-state--maybe-save-places ()
+  "Save places (positions in buffers) if the built-in saveplace package is active."
+  (when (bound-and-true-p save-place-mode)
+    (save-place-alist-to-file)))
+
 (defvar persist-state-supported-packages-alist
   `((bookmark . (:function persist-state--maybe-save-bookmarks))
     (desktop . (:function persist-state--maybe-save-desktop))
@@ -111,7 +116,8 @@
                             :label "Prescient.el"
                             :url "https://github.com/radian-software/prescient.el"))
     (recentf . (:function persist-state--maybe-save-recentf))
-    (savehist . (:function persist-state--maybe-save-savehist)))
+    (savehist . (:function persist-state--maybe-save-savehist))
+    (saveplace . (:function persist-state-maybe-save-places)))
   "A list of packages supported by persist-state.
 
 Each package is a cons cell with the package name and a plist with: