added link to search of ps courses on readme

[dahlsailrunner]

What issue does this PR address?
None - it adds a link to a list of Pluralsight courses (just uses search tag of "serilog") to the readme file.

Does this PR introduce a breaking change?
No

Please check if the PR fulfills these requirements

• The commit follows our guidelines
• Unit Tests for the changes have been added (for bug fixes / features)
  (no unit tests added but not applicable)

Other information:
Only a readme update.

[nblumhardt]

Hi Erik! Thanks for that.

The link won't show me results unless I'm logged into Pluralsight; would https://www.pluralsight.com/search?q=serilog be a better target?

Cheers,
Nick

[dahlsailrunner]

Great catch (I seem to be always logged in haha). I've updated and confirmed that it works. I was wondering about updating the banner at the bottom of the page on https://serilog.net/ -- maybe use the same href and say "these great courses"? I didn't see where to contribute that suggestion on the site. Thanks for the great lib community. :)

[nblumhardt]

Thanks for the reminder about the serilog.net link; I'll zip over and review all the content on that page soon 👍