Issue #1325 Update to the documentation on imporvements to the migration guide

[quarktetra23]

I have read the guidelines for contributing to this open source project.

I have provided a comparison table before the introductions of the type of simulators, an attempt to resolve issue #1325 , please let me know if this needs any updates, or more theory on types of simulators needs to be added.

P.S. I have made some minor wording ad spacing changes too.

[CLAassistant]

All committers have signed the CLA.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[qiskit-bot]

Thanks for contributing to Qiskit documentation!

Before your PR can be merged, it will first need to pass continuous integration tests and be reviewed. Sometimes the review process can be slow, so please be patient. Thanks! 🙌

One or more of the following people are relevant to this code:

• @ElePT
• @beckykd
• @jyu00

[frankharkins]

Thanks! I think this is helpful information. Here's some initial thoughts, our technical writers and subject-matter-experts will have some comments too.

[beckykd]

Good information. Thanks for working on this!

[abbycross]

My suggested changes are mostly changes from camel case to sentence case. Other than that, @beckykd @frankharkins is this ready to merge?