Updated the Readme for the -newline flag

Author: justjanne

README.md

@@ -102,6 +102,8 @@ Usage of powerline-go:
         The list of modules to load. Separate with ','
         (valid choices: cwd, docker, exit, git, hg, host, jobs, perms, root, ssh, user, venv)
         (default "venv,user,ssh,host,cwd,perms,git,hg,jobs,exit,root")
+  -newline
+        Show the prompt on a new line
   -shell string
         Set this to your shell type
         (valid choices: bare, bash, zsh)