fix manual link in header

Author: matthiasdiener

layouts/default.html

@@ -65,7 +65,7 @@
               <li class="dropdown">
 		<a href="#" class="dropdown-toggle" data-toggle="dropdown">Learn <span class="caret"></span></a>
 		<ul class="dropdown-menu" role="menu">
-		  <li><a href="http://charm.cs.illinois.edu/manuals/html/charm++/A.html">Installation</a></li>
+		  <li><a href="https://charm.readthedocs.io/en/latest/charm++/manual.html#installing-charm">Installation</a></li>
       		  <li><a href="/tutorial/">Tutorial</a></li>
 						<li><a href="/exercises/">Exercises</a></li>
       		  <li><a href="/help/">Manual</a></li>

layouts/homepage.html

@@ -65,7 +65,7 @@
               <li class="dropdown">
 		<a href="#" class="dropdown-toggle" data-toggle="dropdown">Learn <span class="caret"></span></a>
 		<ul class="dropdown-menu" role="menu">
-		  <li><a href="http://charm.cs.illinois.edu/manuals/html/charm++/A.html">Installation</a></li>
+		  <li><a href="https://charm.readthedocs.io/en/latest/charm++/manual.html#installing-charm">Installation</a></li>
       		  <li><a href="/tutorial/">Tutorial</a></li>
 						<li><a href="/exercises/">Exercises</a></li>
       		  <li><a href="/help/">Manual</a></li>