Add Note & Warning Blockquote Syntax

[melvincwng]

Is your feature request related to a problem? Please describe.
I noticed that the Note & Warning blockquote syntax isn't in the markdown cheatsheet. Hence, I wish to add the relevant syntax to the repository.

Describe the solution you'd like
I will raise a PR containing the syntax for generating Note & Warning blockquotes in GitHub markdown.

Additional context
Submitting this PR as part of Hacktoberfest 2022 🎉

[melvincwng]

@atapas Hey Tapas, its me Melvin again. Noticed the above issue, while scanning for enhancements & improvements to the existing markdown cheatsheet.

If you would like me to work on it, please kindly assign me this issue & label it with 'hacktoberfest', after which I would proceed to submit a PR with your kind permission :).

Thanks!