Merge Help document to documentation (#1586)

Help document collation (integration of help and documentation documents)

docs/documentation/cn/sql-reference/sql-functions/string-functions/regexp_replace.md

@@ -1,14 +1,13 @@
 # regexp_replace
-
-## Syntax
+## description
+### Syntax
 
 `VARCHAR regexp_replace(VARCHAR str, VARCHAR pattern, VARCHAR repl)
 
-## Description
 
 对字符串 str 进行正则匹配, 将命中 pattern 的部分使用 repl 来进行替换
 
-## Examples
+## example
 
 ```
 mysql> SELECT regexp_replace('a b c', " ", "-");
@@ -25,3 +24,5 @@ mysql> SELECT regexp_replace('a b c','(b)','<\\1>');
 | a <b> c                                |
 +----------------------------------------+
 ```
+##keyword
+REGEXP_REPLACE,REGEXP,REPLACE