Code Improvements

Readability improvements across files

Changed timeout in ‘pxelinux.cfg/default’ to 300 so that users have a
second to breathe and read the menu.

Removed prefixed ‘/‘ in default NETBOOT_FILE arguments because adding
the ‘/‘ just recursively adds it when TFTP server wants to serve
another file.
Example:
First file served -> ‘tftp://file'
Second file served -> ‘tftp:///file'
Third file served -> ‘tftp:////file'

Set iPXE, HTTP, and DHCP as disabled by default and updated README.md
with help to reflect this change.