* add tf2 to howto * update tf2 * remove * modify sidebar * remove quickstart * minor
* fix: update log filepath and branch. * feat: update user guide. * fix: update hadoop user guide * fix: update hadoop user guide
* fix: delete redundant quick examples. * feat: add How-to Guides with use cases. * fix: _toc.yml * fix: fix typo. * fix: fix typo and file location. * fix: add quickstarts to _toc.yml