M3 is missing from addons page

[nonhermitian]

URL, if applicable

https://github.com/Qiskit/qiskit-addon-mthree

Describe the new content you are requesting.

https://github.com/Qiskit/qiskit-addon-mthree

If this new content request is accepted, do you want to write the content?

I will write a draft of the proposed content

[kaelynj]

We'll add this work to #4031