Add cxx-publish-button to the end of main.html

Fix broken links in HTML & PDF output

Author: jaredhoberock

main.html

@@ -12,6 +12,7 @@
 <cxx-include href="execution_policies.html"></cxx-include>
 <cxx-include href="exceptions.html"></cxx-include>
 <cxx-include href="algorithms.html"></cxx-include>
+<cxx-publish-button source="https://github.com/cplusplus/parallelism-ts"></cxx-publish-button>
 
 </body>
 </html>