Very minor fixes

Love the theme. I made two very small changes here.

1. `_config.yml` was spelled `config.yml` in the README. I corrected the typo.
2. The LinkedIn link format wasn't working for me. I'm guessing that their URL format changed since you wrote the code. I modified the footer and the `_config.yml` example to take an entire LinkedIn profile link instead of just a username just like StackExchange does. I couldn't find your LinkedIn profile so I used firstname-lastname for the example ;).