[Documentation] Added documentation page for vcpkg_fixup_cmake_targets.cmake

[vpaladino778]

Added example usage comment to .cmake file. I found it somewhat confusing with the way the comment was formatted, so i changed it for clarity. Also added a basic documentation page for vcpkg_fixup_cmake_targets.cmake

[vicroms]

LGTM

[cbezault]

/azp run

[vpaladino778]

I'm trying to figure out why @cbezault's commits caused the build to fail, because my original commit passed the tests. The weird thing is that all he changes was some comments.

[vpaladino778]

Here was the errors from the failed checks:

##[error] REGRESSION: librabbitmq:x64-linux
##[error] REGRESSION: geographiclib:x64-linux
##[error] REGRESSION: otl:x64-linux

After checking out the master branch, and attempting to compile geographiclib and otl, I recieved errors. So this problem may not be with these commits, but a problem with the master branch.

[cbezault]

I'm pretty sure otl's hash changed on us, which is why it's failing :/.
Ideally we would clean up all these failures in other PRs and then merge this one.

[azure-pipelines]

Commenter does not have sufficient privileges for PR 8365 in repo microsoft/vcpkg