Improve syntax highlighting in README

Add `bash` hint to shell commands in README in order to improve the
syntax highlighting.

Change-Id: Iab0087f244e94be26fa5ccd9fa40f4784a1d3cf2
Reviewed-on: https://gerrit.causes.com/28454
Tested-by: Shane da Silva <shane@causes.com>
Reviewed-by: Greg Hurrell <greg@causes.com>