Clean up README

[garrettbyrd]

The README has some minor spots which could be cleaned up. Mainly utilizing #> instead of triple ticks for code blocks. E.g.,

#> make

should be

make

for improved readability.

This PR also includes the usage of GitHub's markdown alert syntax for notes and warnings.

[garrettbyrd]

@sumachidanand @nchatrad Are you interested in this revision?

[sumachidanand]

Hi,

Thank you for the commit. This change looks good, We are evaluating to apply this to our tree,