Update README.md
Fix: error 500

When you have already set index.php as default, you get a error 500. 
So first you need to remove it then add it again. This is solving the error 500.
Merge pull request #2 from 810/patch-1

Fix: error 500 IIS - Thanks!
Make images progressive by default
Update system default settings to be more suitable for production
Exit instead of throwing exception when PHP < 5.4.0
Better error message when template file isn't found
Fix PHP warning on locking without file handle
Added Contributing section
Update README.md
Fixed typos/CS
Merge pull request #3 from pborreli/typos

Fixed typos/CS
Merge branch 'develop' of github.com:getgrav/grav into feature/asset_management