Rename some main section title

Signed-off-by: Benoit Donneaux <benoit@leastauthority.com>

src/index.html

@@ -13,7 +13,7 @@ excerpt: >-
   Even if some of the servers fail or are taken over by an attacker,
   the entire file store continues to function correctly, preserving your privacy and security.
 documentation:
-  - title: "Read Some Nice Docs"
+  - title: "Documentation"
 documentation_list:
   - image_path: /assets/images/overview.png
     alt: "overview"
@@ -36,7 +36,7 @@ documentation_list:
       <li><a href="https://tahoe-lafs.org/trac/tahoe-lafs/wiki/FAQ">Frequently Asked Questions</a></li>
     </ul>'
 contribute:
-  - title: "Get Involved"
+  - title: "Contribute"
     excerpt: ""
 contribute_list:
   - image_path: /assets/images/discussions.png