Update documentation for drbd8 and beta2 release

This patch does:
  - add drbd8 information to the docs (the new disk template, examples,
    etc.)
  - fixes a section header to make it more clear
  - update the NEWS file by changing format (format taken by looking at
    /usr/sharea/doc/*/NEWS.gz) and adding more information on changes
    since beta1

Reviewed-by: ultrotter