Add doc in https://github.com/redhat-developer/vscode-xml/blob/master/docs/Extensions.md#custom-xml-extensions with https://github.com/OpenLiberty/liberty-language-server/pull/34#issuecomment-742524222
Add doc in https://github.com/redhat-developer/vscode-xml/blob/master/docs/Extensions.md#custom-xml-extensions with OpenLiberty/liberty-language-server#34 (comment)