Detect the presence of .htaccess files and display a warning about them being ignored

[lolautruche]

Documentation already tries to make it clear that we're not using Apache but Nginx for the webserver. Therefore, htaccess files are not taken into account (but it's at the bottom of a very long page).

One idea (starring @gilzow) would be to detect if .htaccess files are present in the codebase with Platformify, and display a warning that they'll be ignored as Platform.sh is using Nginx. We may limit the check to the root and webroot directories.

[gilzow]

i think limiting to the root/webroot directories is a perfectly acceptable solution.