XCC install directions need updating in boards/xtensa/intel_s1000_crb/doc/index.rst

[galak]

The instructions for install XCC need some minor updates to be complete:

1. Missing how to setup/install the license file.

2. File name referenced is not correct:
   X6H3SUE_2016_4_linux_redist.tgz should be: 2018-05-15_5afafc055d3f4_X6H3SUE_2016_4_linux_redist.tgz

3. The tar command possible needs to be run with 'sudo'

[galak]

Possible comment about needing libnsl.i686 on fedora (was missing and causing some issues).