EZP-23339: use correct 'xargs sudo chmod' order

JIRA: https://jira.ez.no/browse/EZP-23339

This is a nitpick on the install doc: instead of running `xargs` as sudo, only run the actual (chmod) command.

In addition, AFAICT `sudo find` seems unnecessary - any user with access to ezproot should have read permissions for the remainder of the necessary files/folders, in which case simply `find` is sufficient.