Added important disambiguation to swarm mode (#10987)

* Added important disambiguation to swarm mode

This really needs to be added, I had no idea people gave up on docker/swarm because of a misunderstanding, but it's common enough we need to clarify it.

From Docker's public #swarm slack channel:
```
andrew grosser  4:45 PM
Hey @channel I am about to give a talk in San Francisco to a bunch of devops experts about swarm using my ingress and reverse proxy controller https://github.com/sfproductlabs/roo and one of the organizers said swarm was deprecated, is that so? It's so much easier than kubernetes, I can't imagine losing it.
sfproductlabs/roo
A zero config distributed edge-router & reverse-proxy (supporting multiple letsencrypt/https hosts). No dependencies.
Stars
40
Language
Go
<https://github.com/sfproductlabs/roo|sfproductlabs/roo>sfproductlabs/roo | Apr 9th | Added by GitHub
4:46
Is there something we don't know?
james_wells  4:48 PM
As of the most recent official Docker release, no Swarm is still officially part of Docker...  They merely added native support for Kubernetes
andrew grosser  4:49 PM
🙏 Phew, is there an EOL?
4:49
Thanks @james_wells
4:50
I think they going to get the grenade launchers out if I can't answer these questions
james_wells  4:51 PM
Now that is a good question and my guess is that no, there is no plan to remove it, at least before Docker 3.
andrew grosser  4:52 PM
Amazing thx, I have a system that is a startups dream and is personally saving me more than 10x using swarm, so praying it stays
bmitch:docker:  4:53 PM
Classic container deployed swarm is deprecated (I believe). Swarm mode that's integrated into the engine is still being developed by Mirantis with no EOL set.
4:53
So if someone says swarm is deprecated, make sure to ask "which swarm" they are referring to.
andrew grosser  4:54 PM
Ok thanks @bmitch
4:54
Think that's a brand thing we'll need to help change
james_wells  4:56 PM
@bmitch I am not sure I understand what you are sayin there.  Could you please explain the differences
bmitch:docker:  4:56 PM
See the disambiguation section: https://hub.docker.com/r/dockerswarm/swarm
james_wells  4:57 PM
Excellent.  Thank you sir
andrew grosser  5:02 PM
Thanks
bmitch:docker:  5:02 PM
See also this link where they are getting ready to archive the standalone swarm, aka classic swarm. https://github.com/docker/classicswarm/issues/2985#issuecomment-640486361
justincormackjustincormack
Comment on #2985 Why have all issues been closed?
The vast majority of issues were from 5 years ago when it was being actively developed, and the recent ones were all mistakes for swarmkit, other than some issues I resolved. Many were issues in components or Moby or other software and may be resolved. It is GitHubs (reasonable) recommendation that you close issues and PRs before archiving a repository so that people know they are not being worked on, and I was also looking to see if anyone came forward to say that they were still working on things or, indeed, actively using Swarm Classic.
<https://github.com/docker/classicswarm|docker/classicswarm>docker/classicswarm | Jun 8th | Added by GitHub
james_wells  5:08 PM
That is really unfortunate...  Kubernetes is simply too expensive IMNSHO, Swarm is nice and lightweight.
andrew grosser  5:08 PM
Both the different swarms point to the same point in the documentation in the disambiguation @bmitch
bmitch:docker:  5:09 PM
Swarm mode, aka swarmkit is alive and well.
andrew grosser  5:10 PM
Whoa I can see why they were confused
bmitch:docker:  5:10 PM
If you type docker swarm init you are not running classic swarm
andrew grosser  5:11 PM
Can someone inside docker add this to the swarm docs page? I think it's important
5:12
I think something talking about 2014 was EOLd but this is still current and alive would help.
bmitch:docker:  5:12 PM
Docker themselves isn't maintaining it, that team went to Mirantis, so someone over there would need to submit the PR
andrew grosser  5:12 PM
OK, could I?
bmitch:docker:  5:13 PM
Docs are in GitHub
andrew grosser  5:13 PM
Thanks
```

* Minor edit to the wording to clarify the diff

* Minor update

Co-authored-by: Usha Mandya <47779042+usha-mandya@users.noreply.github.com>

engine/swarm/index.md

@@ -52,6 +52,10 @@ Current versions of Docker include *swarm mode* for natively managing a cluster
 of Docker Engines called a *swarm*. Use the Docker CLI to create a swarm, deploy
 application services to a swarm, and manage swarm behavior.
 
+Docker Swarm mode is built into the Docker Engine. Do not confuse Docker Swarm mode
+with [Docker Classic Swarm](https://github.com/docker/classicswarm){:target="_blank" rel="noopener" class="_"}
+which is no longer actively developed.
+
 ## Feature highlights
 
 * **Cluster management integrated with Docker Engine:** Use the Docker Engine