opt: update doc (#1861)

* doc: update doc

website/docs/ui_fulltextsearch.md

@@ -8,9 +8,8 @@ Type the desired word in "Search line" to search.
 
 Search modes
 
-* "Default" — This follows the [xapian search syntax](https://xapian.org/docs/queryparser.html). Note that phrase searching and NEAR operator needs `Enable index with positional information` enabled at settings.
-* "Plain text" - mode like "Whole words" but every word in search line can be treated as word fragment.
-* "Wildcards" - the search line contains a Unix-like template. Such template can contain wildcard symbols `?` (matches any one character), `*` (matches any character number) or ranges of characters `[...]` To find characters `?`, `*`, `[` and `]` it should be escaped by backslash like `\?`, `\*`, `\[`, `\]`.
+* "Default" — This follows the [xapian search syntax](https://xapian.org/docs/queryparser.html). 
+* "Wildcards" - xpaian "wildcard" mode, which means it only supports the prefix wildcards like "hell*"(in English alike language).As CJK use NGRAM term generator,the `*` should be treated as a seperator while not quoted.
 
 "Available dictionaries in group" - here you can view how many dictionaries in the current group are suitable for full-text search, how many dictionaries already indexed and how many dictionaries wait for indexing.