Add basic terminology page for SIG-MC.

[lauralorenz]

Add a terminology.md page in the community repo for SIG-Multicluster that gives a bare-bones list of terminology and their alternate names, and provides a link out to the website for more information.

Which issue(s) this PR fixes:

No issue, but based off of conversation in #8210 (comment).

[RainbowMango]

/lgtm
Thank you, Laura.

[pacoxu]

/assign @JeremyOT @skitt

[lauralorenz]

Updated to not have ClusterProperty in "previously known as" section for About API to align with community feedback re: kubernetes-sigs/sig-multicluster-site#41 (comment), but I couldn't resist adding in a true "previously known as" for that one, ClusterClaim 😄

[lauralorenz]

@RainbowMango now that I have resolved #8536 (comment) (for now hehe), will you lgtm if everything else is ok?

[RainbowMango]

/lgtm

Thanks @lauralorenz

I guess this is ready to move forward now.

Once this PR has been reviewed and has the lgtm label, please ask for approval from jeremyot.

cc @JeremyOT for approval
also cc @skitt

[skitt]

/approve

Thanks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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