Include some legal contents in website (#10491)

Summary:
We are asked to include TOS, Privacy Policy and copyright in the website. Added it.
Also changed the github and twitter link to RocksDB's rather than Facebook Open Source's and link to Meta open source's home page.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10491

Test Plan: Test the website locally.

Reviewed By: jay-zhuang

Differential Revision: D38475212

fbshipit-source-id: f73622f8f3d361b4586221ffb6deac4f4a11bb15

docs/_includes/footer.html

@@ -9,15 +9,16 @@
               <path class="logoRing innerRing" d="M 484.9 424.4 c 69.8 -2.8 133.2 57.8 132.6 132 C 617 630 558.5 688.7 484.9 689.1 c -75.1 0.4 -132.6 -63.6 -132.7 -132.7 C 352.1 485 413.4 421.5 484.9 424.4 Z M 401.3 556.7 c -3.4 37.2 30.5 83.6 83 84.1 c 46.6 0.4 84.8 -37.6 84.9 -84 c 0.1 -46.6 -37.2 -84.4 -84.2 -84.6 C 432.2 472.1 397.9 518.3 401.3 556.7 Z" />
             </g>
           </svg>
-        <h2>Facebook Open Source</h2>
+        <h2><a href="https://opensource.fb.com/" target="_blank">Meta Open Source</a></h2>
       </div>
       <div class="footerSection">
-        <a class="footerLink" href="https://code.facebook.com/projects/" target="_blank">Open Source Projects</a>
-        <a class="footerLink" href="https://github.com/facebook/" target="_blank">GitHub</a>
-        <a class="footerLink" href="https://twitter.com/fbOpenSource" target="_blank">Twitter</a>
+        <a class="footerLink" href="https://github.com/facebook/rocksdb" target="_blank">GitHub</a>
+        <a class="footerLink" href="hhttps://twitter.com/rocksdb" target="_blank">Twitter</a>
+        <a class="footerLink" href="https://opensource.fb.com/legal/terms" target="_blank">Terms of Use</a>
+        <a class="footerLink" href="https://opensource.fb.com/legal/privacy" target="_blank">Privacy Policy</a>
       </div>
       <div class="footerSection rightAlign">
-        <a class="footerLink" href="https://github.com/{{ site.ghrepo }}" target="_blank">Contribute to this project on GitHub</a>
+       Copyright © 2022 Meta Platforms, Inc.
       </div>
     </div>
   </div>