Fix typos in README.md

[itsdeannat]

Copy edited the following:

• Added serial commas
• Added comma after introductory phrase "for example"
• Fix typo: in this separated page > in this separate page
• Fix typo and sentence structure under "ML.NET videos playlist at YouTube" section
• Fix wording: or alternatively > alternatively

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We are excited to review your PR.

So we can do the best job, please check:

• There's a descriptive title that will make sense to other developers some time from now.
• There's associated issues. All PR's should have issue(s) associated - unless a trivial self-evident change such as fixing a typo. You can use the format Fixes #nnnn in your description to cause GitHub to automatically close the issue(s) when your PR is merged.
• Your change description explains what the change does, why you chose your approach, and anything else that reviewers should know.
• You have included any necessary tests in the same PR.

[najeeb-kazmi]

@deanna-cs please pull master, so that you have this commit. With this, the randomly failing tests will be skipped, so we can merge this PR.

[itsdeannat]

@najeeb-kazmi Done