Improve PR instructions

[BillyONeal]

• Get update contributors to check boxes they actually did because they were vacuous.
• Get people claiming that they comply with the naming policy to prove it. There have been WAY too many people checking this box without actually doing it recently.
• Suggest VCPKG_LOCK_FIND_PACKAGE. Thanks @dg0yt !
• Acknowledge the existence of ci.feature.baseline.txt.
• Note that a usage file should not be added if the automatic one works.

[BillyONeal]

Example new port "zlib":

• Changes comply with the maintainer guide.
• The name of the port meets one of the following alternatives:
  • This component on https://repology.org/ is https://repology.org/project/zlib/versions
  • This component is strongly associated with that name in web searches of the name, or "name c++". Include a screenshot of the search engine results in the PR.
  • This component follows the 'GitHubOrg-GitHubRepo' form
• Optional dependencies are resolved in exactly one way. For example, if the component is built with CMake, all find_package calls are REQUIRED, are satisfied by vcpkg.json's declared dependencies, or controlled with CMAKE_DISABLE_FIND_PACKAGE_Xxx or VCPKG_LOCK_FIND_PACKAGE.
• The versioning scheme in vcpkg.json matches what upstream says.
• The license declaration in vcpkg.json matches what upstream says.
• The installed as the "copyright" file matches what upstream says.
• The source code of the component installed comes from an authoritative source.
• The generated "usage text" is brief and accurate. See adding-usage for context. Don't add a usage file if the default generated usage is correct.
• The version database is fixed by rerunning ./vcpkg x-add-version --all and committing the result.
• Exactly one version is added in each modified versions file.