Add notice to the ROS 2 and RTI Connext documentation (backport #227)

[mergify]

Description

Add notice about official ROS 2 and RTI Connext documentation to the README.

Is this user-facing behavior change?

Users will now have a direct link to the official ROS 2 and RTI Connext documentation in the README, with the most up-to-date information.

Did you use Generative AI?

No

Additional Information

---

This is an automatic backport of pull request #227 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 3dbef7c has failed:

On branch mergify/bp/kilted/pr-227
Your branch is up to date with 'origin/kilted'.

You are currently cherry-picking commit 3dbef7c.
  (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:   README.md

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

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[ahcorde]

@fgallegosalido do you mind to fix the conflicts ?

[fujitatomoya]

@fgallegosalido does this need to backport to kilted?

[fgallegosalido]

@fujitatomoya yes. The documentation referenced starts at Kilted, so having the notice in the kilted branch can be really helpful for users that come by. I'll fix the conflicts as soon as possible.