Update documentation to point to new default DDS (bp #1000)

[mergify]

This is an automated backport of pull request #1000 done by Mergify

Cherry-pick of 1edebe3 has failed:

On branch mergify/bp/rolling/pr-1000
Your branch is up to date with 'origin/rolling'.

You are currently cherry-picking commit 1edebe3.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   source/Tutorials/Working-with-multiple-RMW-implementations.rst

no changes added to commit (use "git add" and/or "git commit -a")

To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

Mergify commands and options

More conditions and actions can be found in the documentation.

You can also trigger Mergify actions by commenting on this pull request:

• @Mergifyio refresh will re-evaluate the rules
• @Mergifyio rebase will rebase this PR on its base branch
• @Mergifyio update will merge the base branch into this PR
• @Mergifyio backport <destination> will backport this PR on <destination> branch

Additionally, on Mergify dashboard you can:

• look at your merge queues
• generate the Mergify configuration with the config editor.

Finally, you can contact us on https://mergify.io/

[clalancette]

Going ahead and merging this one with the conflict fixed.

[maryaB-osr]

@clalancette This should not have created automatic backports to foxy and dashing; only one of the pages matched the "common pages" rule. Previously when I tested this case (PR with one or more common pages but also other pages), mergify didn't create backports, so I thought we were good to go. I'll have to look at the mergify rules, but this could be pretty bad/annoying if it can't be fixed :/