doghouse: add more description in /gh/
</p>
<p>
Go to https://reviewdog.app/gh/{owner}/{repo} to get REVIEWDOG_TOKEN.
+ <br>
+ Or
+ <br>
+ Run reviewdoc CLI from Travis CI without REVIEWDOG_TOKEN.
+ <br>
+</p>
+<p>
+ <pre>
+$ reviewdog -conf=.reviewdog.yml -reporter=github-pr-check
+ </pre>
+ See also <a href="https://github.com/haya14busa/reviewdog">github.com/haya14busa/reviewdog</a>
</p>
