Protect example.cfg from accidental commits to a public repository

In working with the provided example, I realized that potentially sensitive information (even if it's only the address of a SAML provider) may inadvertently be committed to a public repository if the user edits example.cfg directly. This pull request moves the provided example.cfg to example.cfg.dist and instructs the user to copy the file and then edit. Also, example.cfg and likely certificate files are now blocked in .gitignore.