doc: fix broken links after content reorg

Home page "button" links needed to be manually updated (because of the
raw html usage) after content around.

Move partition mode docs from try to develop persona pages.

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>

doc/index.rst

@@ -16,7 +16,7 @@ through an open source platform.
 
    <ul class="grid">
        <li class="grid-item">
-           <a href="learn/index.html">
+           <a href="learn.html">
                <img alt="" src="_static/images/ACRNlogo.png"/>
                <h2>Learn about<br/>ACRN</h2>
            </a>
@@ -24,7 +24,7 @@ through an open source platform.
               features, and use-case scenarios</p>
        </li>
        <li class="grid-item">
-           <a href="try/index.rst">
+           <a href="try.html">
                <span class="grid-icon fa fa-map-signs"></span>
                <h2>Try using<br/>ACRN</h2>
            </a>
@@ -32,7 +32,7 @@ through an open source platform.
               samples</p>
        </li>
        <li class="grid-item">
-           <a href="develop/index.html">
+           <a href="develop.html">
                <span class="grid-icon fa fa-cogs"></span>
                <h2>Develop using<br/>ACRN</h2>
            </a>
@@ -40,7 +40,7 @@ through an open source platform.
               solutions</p>
        </li>
        <li class="grid-item">
-           <a href="contribute/index.html">
+           <a href="contribute.html">
                <span class="grid-icon fa fa-github"></span>
                <h2>Contribute to<br/>ACRN</h2>
            </a>