Rename moby/conatinerd project

[free2create]

What is the problem you're trying to solve
Now that moby/containerd has no explicit fork relationship with containerd/containerd as an upsteam/downsteam repo,
users can be easily confuse moby/containerd with the official, very active containerd/containerd

Describe the solution you'd like
Pick a new name.
First steps would be to :

1. Announce it at the very TOP of the README.md that this project is an independent project.
2. Choose a new name, but only update the README,md
3. Rename the github repo to new name.
4. Optional: Go all the way and change the namespace of the codebase.

Additional context
Just steps 1 & 2 are sufficient for full disclosure.
Step 3 should also be relatively painless and transparent to the 7 users who have forked this project.
I assume Step 4 would be costly/painful and really isn't needed unless this project grows further.

[tianon]

I don't have a lot of privileges on this repo, but apparently enough to change the description and website metadata, so I've done that now in a way that hopefully makes the repository status/purpose more clear (with an explicit pointer to https://github.com/containerd/containerd).