Added link to download vim-gnupg plugin

README.md

@@ -37,6 +37,8 @@ then append ".gpg" to each note name, for example
 
 To install, place `vns` in your path, 
 
+** Note: ** Install [vim-gnupg] before use.
+
 To uninstall, remove the files you copied. Notes will still exist in $HOME/.local/vns
 
 Once installed, VNS will require you to run `sns -i [gpgkey]`, to indicate you would like
@@ -69,3 +71,4 @@ Feature requests should be submitted to jon.lewis@xenami.net with [SNS Feature R
 in the subject line.
 
 [pass]: http://passwordstore.org
+[vim-gnupg]:http://www.vim.org/scripts/script.php?script_id=3645