improve document

Author: wxiaoguang

custom/conf/app.example.ini

@@ -700,6 +700,7 @@ LEVEL = Info
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Git config options
+;; This section only does "set" config, a removed config key from this section won't be removed from git config automatically
 ;[git.config]
 ;diff.algorithm = histogram
 ;other.config-key = ...

docs/content/doc/administration/config-cheat-sheet.en-us.md

@@ -1070,7 +1070,8 @@ Default templates for project boards:
 
 ### Git - Config options (`git.config`)
 
-The key/value pairs in this section will be used as git config:
+The key/value pairs in this section will be used as git config.
+This section only does "set" config, a removed config key from this section won't be removed from git config automatically.
 
 - `diff.algorithm`: **histogram**
 - `other.config-key`: ...