Merge pull request #3898 from dvarrazzo/socket-dir-docs

Fixed location of the IPC socket in the docs

docs/userguide

@@ -1005,7 +1005,8 @@ programs to get information from i3, such as the current workspaces
 (to display a workspace bar), and to control i3.
 
 The IPC socket is enabled by default and will be created in
-+/tmp/i3-%u.XXXXXX/ipc-socket.%p+ where +%u+ is your UNIX username, +%p+ is
++$XDG_RUNTIME_DIR/i3/ipc-socket.%p+ if the directory is available, falling back
+to +/tmp/i3-%u.XXXXXX/ipc-socket.%p+, where +%u+ is your UNIX username, +%p+ is
 the PID of i3 and XXXXXX is a string of random characters from the portable
 filename character set (see mkdtemp(3)).