Document a function to conditionally map LC funcs

Author: cmcaine

doc/LanguageClient.txt

@@ -35,6 +35,19 @@ like to map these functions to shortcuts, for example: >
     nnoremap <silent> gd :call LanguageClient#textDocument_definition()<CR>
     nnoremap <silent> <F2> :call LanguageClient#textDocument_rename()<CR>
 
+You can apply these mappings only for buffers with supported filetypes with a
+simple function: >
+
+    function LC_maps()
+      if has_key(g:LanguageClient_serverCommands, &filetype)
+        nnoremap <buffer> <silent> K :call LanguageClient#textDocument_hover()<cr>
+        nnoremap <buffer> <silent> gd :call LanguageClient#textDocument_definition()<CR>
+        nnoremap <buffer> <silent> <F2> :call LanguageClient#textDocument_rename()<CR>
+      endif
+    endfunction
+
+    autocmd FileType * call LC_maps()
+
 If one is using deoplete/nvim-completion-manager at the same time, completion
 should work out of the box. Otherwise, completion is available with 'C-X C-O'
 ('omnifunc').