Docs: update docs

Author: yujiangshui

docs/.gitignore

@@ -1,4 +1,3 @@
 .DS_Store
-gitbook
 _book
 node_modules/

docs/essence/index.html

@@ -350,7 +350,7 @@ <h1 class="search-results-title">No results matching "<span class='search-query'
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