NOTES.txt and .tpl files

[luisdavim]

This would improve the syntax highlight of those files as well as the use of the helm language server, see: mrjosh/helm-ls#82

[qvalentin]

.tpl is already supported, for .txt you can just add another pattern here: https://github.com/towolf/vim-helm/blob/master/ftdetect/helm.vim#L1

[towolf]

Closed as per #22