Added release note about fixing CDAP-1086, "Fixed a problem with the readless increment implementation..."
Adding fixing of CDAP-1044 (Upgrade tool)
Merge branch 'release/2.6.0' into feature/r2.6.0_fix_release_notes
Improve formatting and example for Docker.
Fix reference.
Merge pull request #869 from caskdata/feature/r2.6.0_fix_release_notes

CDAP-1044, 1062: Added to release notes about fixing CDAP-1044, CDAP-1062