added note that control port must be enabled and how to do that in to…

…rrc config file

doc/tor.md

@@ -93,7 +93,7 @@ API, to create and destroy 'ephemeral' hidden services programmatically.
 Bitcoin Core has been updated to make use of this.
 
 This means that if Tor is running (and proper authentication has been configured),
-Bitcoin Core automatically creates a hidden service to listen on. This will positively 
+Bitcoin Core automatically creates a hidden service to listen on. This will positively
 affect the number of available .onion nodes.
 
 This new feature is enabled by default if Bitcoin Core is listening (`-listen`), and
@@ -102,8 +102,9 @@ and, if not disabled, configured using the `-torcontrol` and `-torpassword` sett
 To show verbose debugging information, pass `-debug=tor`.
 
 Connecting to Tor's control socket API requires one of two authentication methods to be
-configured. For cookie authentication the user running bitcoind must have write access
-to the `CookieAuthFile` specified in Tor configuration. In some cases, this is
+configured. It also requires the control socket to be enabled, e.g. put `ControlPort 9051`
+in `torrc` config file. For cookie authentication the user running bitcoind must have read
+access to the `CookieAuthFile` specified in Tor configuration. In some cases this is
 preconfigured and the creation of a hidden service is automatic. If permission problems
 are seen with `-debug=tor` they can be resolved by adding both the user running Tor and
 the user running bitcoind to the same group and setting permissions appropriately. On