am 21111c2c: am f7a8c0f7: cherrypick Change-Id: Icf0c7772901f742c36ba417e07cc5e299f72849a fix broken links, update the dev guide intro, and update sitemap file

* commit '21111c2cddff2a62b2de0afe9e70607cc4054e54':
  cherrypick Change-Id: Icf0c7772901f742c36ba417e07cc5e299f72849a fix broken links, update the dev guide intro, and update sitemap file