add note regarding pch.h files

[rtischer8277]

For a lot of us devs who generated MFC projects years ago, (re)generating new MFC projects create a pch.h header instead of a stdafx.h file. pch.h files include windows header files, but operate differently. This topic should be introduced and I can think of no better way than to address head on how to make CString compile.
The Note I wrote needs to be formatted, for example, with green background.
By the way, I did submit feedback to the Developer Community about this, so maybe they will weigh in on the correct approach to all this. See Unable to compile with MFC CString using new pch.h.

[PRMerger6]

@rtischer8277 : Thanks for your contribution! The author(s) have been notified to review your proposed change.

[jborsecnik]

@TylerMSFT,

Can you review the proposed changes? Note that the "Note" will have to be changed to the Docs-standard formatting for notes.

IMPORTANT: When the changes are ready for publication, add a #sign-off comment to signal that the PR is ready for the review team to merge. Thanks.

#label:"aq-pr-triaged"
#assign:@MicrosoftDocs/public-repo-pr-review-team

[PRMerger18]

The following users don't have valid GitHub IDs, or are not collaborators on this repo: microsoftdocs/public-repo-pr-review-team

[TylerMSFT]

#hold-off
Hi @rtischer8277, thank you for adding to the docs. I need to think about this one first and I'm in the middle of another project. I will circle back to this as soon as I have some time to do so.

[rtischer8277]

I think the pch.h CString Note and I am reporting here is a compiler bug and doesn't need a doc Note. CString is properly defined when generating an MFC project using the MFC App template, but not when generating a Dynamic-Link Library set to Using MFC.... I have indicated this change in Unable to compile with MFC CString using new pch.h.

[TylerMSFT]

Thanks for logging the bug, @rtischer8277