Update in the Readme

When I tried to symlink I got such error:
```text
$ homesick symlink lubieniebieski/vim-castle                                                                                                                                                                                                                                                                                *[master]
       error  Could not symlink lubieniebieski/vim-castle, expected /Users/oskarlakner/.homesick/repos/lubieniebieski/vim-castle/home exist and contain dotfiles
```