add information on Go HTML template

Author: aitva

README.md

@@ -34,6 +34,7 @@ Tutorial for vim-go. A simple tutorial on how to install and use vim-go.
 14. [Generate it](#generate-it)
   * [Method stubs implementing an interface](#method-stubs-implementing-an-interface)
 15. [Share it](#share-it)
+16. [HTML template](#html-template)
 
 # Quick Setup
 
@@ -2175,6 +2176,16 @@ can manually set the browser via:
 let g:go_play_browser_command = "chrome"
 ```
 
+# HTML template
+
+`vim-go` comes with syntax highlighting for Go HTML template. By default it
+is enabled for `.tmpl` files. If you want to enable it for another filetype
+add the following setting to your `.vimrc`:
+
+```
+au BufRead,BufNewFile *.gohtml set filetype=gohtmltmpl
+```
+
 # Donation
 
 This tutorial was created by me in my spare time. If you like it and would