dev/index: add related-box with link to docs overview

Optimize the open sign, and don't show it on the index page (since it
made showing the related box complicated).

Author: bagder

dev/_index.html

@@ -15,24 +15,21 @@
 WHERE1(Development)
 
 TITLE(Developing curl)
-<div class="featurewindow">
-  The <b>Feature window</b> is now<br>
-  <a href="feature-window.html">
-#if FEATUREWINDOW
-  <img src="../pix/open-sign.svg" alt="Featurewindow open"
-#else
-  <br><img src="../pix/closed-sign.svg" alt="Featurewindow closed"
-#endif
-        class="featurewindowsign">
-  </a>
+<div class="relatedbox">
+<b>Related:</b>
+<br><a href="/docs/">Docs Overview</a>
 </div>
 <p>
  This is the section of the website devoted to the development of curl and
- libcurl. If you are a "user" of curl or libcurl, this may not be where you
- want to hang out.
+ libcurl. There is always development going on in the curl project.
+
 <p>
- There is always development going on in the curl project. To help out the
- development team, we provide these services:
+ The <a href="feature-window.html">feature window</a> is now
+#if FEATUREWINDOW
+ <b>open</b>.
+#else
+ <b>closed</b>.
+#endif
 
 SUBTITLE(Generated contents)
 <p>