Some of the notes and readme files have been converted to markdown
format recently and renamed during this process. While adding the
.md extension was a natural step, switching to mixed cases was not
a change to the better, it gives them a ragged appearance:

     NOTES.ANDROID  => NOTES-Android.md
     NOTES.DJGPP    => NOTES-DJGPP.md
     NOTES.PERL     => NOTES-Perl.md
     NOTES.UNIX     => NOTES-Unix.md
     NOTES.VMS      => NOTES-VMS.md
     NOTES.VALGRIND => NOTES-Valgrind.md
     NOTES.WIN      => NOTES-Windows.txt
     README.ENGINE  => README-Engine.md
     README.FIPS    => README-FIPS.md

Moreover, the NOTES-Windows.txt file is the only file which has been
converted to markdown but has received a .txt file extension.
This doesn't make sense, because the OpenSSL users on Windows will
need to read the other markdown documents as well. Since they are
developers, we can trust them to be able to associate their favorite
editor with the .md extension.

In fact, having a comment at the beginning of the file saying that it
is in markdown format but we didn't dare to add the correct extension
in order not to overwhelm our Windows users can be interpreted either
as unintentionally funny or disrespectful ;-)

This commit suggests the following more consistent renaming:

     NOTES.ANDROID  => NOTES-ANDROID.md
     NOTES.DJGPP    => NOTES-DJGPP.md
     NOTES.PERL     => NOTES-PERL.md
     NOTES.UNIX     => NOTES-UNIX.md
     NOTES.VMS      => NOTES-VMS.md
     NOTES.VALGRIND => NOTES-VALGRIND.md
     NOTES.WIN      => NOTES-WINDOWS.md
     README.ENGINE  => README-ENGINES.md
     README.FIPS    => README-FIPS.md

(note the plural in README-ENGINES, anticipating a README-PROVIDERS)

Reviewed-by: Paul Dale <[email protected]>
(Merged from #14042)

Formatting is still very mixed in the NOTES and README files.
This commit tries to make formatting more consistent with the one
introduced in pull request #10545.

Reviewed-by: Paul Dale <[email protected]>
(Merged from #14042)

In many locations, the files have been converted to markdown
syntactically, but don't utilize the power of markdown yet.
Here, instead of just repeating the file name, the markdown link
now shows the title of the document.

Additionally, the notes are now reference in the same order in both
the README and the INSTALL file.

Reviewed-by: Paul Dale <[email protected]>
(Merged from #14042)

Reviewed-by: Paul Dale <[email protected]>
(Merged from #14042)

The current content of this README file are just meant to be a
starting point and an incentive to add more. Most of the text
was borrowed from the [OpenSSL 3.0 Wiki], which is the reason
why a added Matt as co-author. To be continued...

[OpenSSL 3.0 Wiki]: https://wiki.openssl.org/index.php/OpenSSL_3.0

Co-authored-by: Matt Caswell <[email protected]>

Reviewed-by: Paul Dale <[email protected]>
(Merged from #14042)

CLA: trivial

(cherry picked from commit fb97b8e)

Reviewed-by: Paul Dale <[email protected]>
Reviewed-by: Matthias St. Pierre <[email protected]>
(Merged from #14042)