Add pull request manually merge instruction (#13840)

* add pull request command line instructions

* Add pull request manually merge instuction

* Fix styles

* Fix lint

* Move inline style to class file

* add space between merge button and hint text

* Add sentence end charcter

* Change the language file

* adjust secondary bg

* further adjustment

Co-authored-by: silverwind <me@silverwind.io>

web_src/less/helpers.less

@@ -1,5 +1,7 @@
 .df { display: flex !important; }
+.di { display: inline !important; }
 .dif { display: inline-flex !important; }
+.dib { display: inline-block !important; }
 .ac { align-items: center !important; }
 .tc { text-align: center !important; }
 .jc { justify-content: center !important; }