Fix#36726
### Changes
* Patch `easyloggingpp/CMakeLists.txt` to change
`ELPP_PKGCONFIG_INSTALL_DIR` from `share/pkgconfig` to `lib/pkgconfig`.
* Patch `easyloggingpp/cmake/easyloggingpp.pc.cmakein` to add `libdir`
and `Libs`
* Add `usage` about `FindPkgConfig` module
### Checklist
- [x] Changes comply with the [maintainer
guide](https://github.com/microsoft/vcpkg-docs/blob/main/vcpkg/contributing/maintainer-guide.md).
- [ ] SHA512s are updated for each updated download.
- [ ] ~The "supports" clause reflects platforms that may be fixed by
this new version.~
- [ ] Any fixed [CI
baseline](https://github.com/microsoft/vcpkg/blob/master/scripts/ci.baseline.txt)
entries are removed from that file.
- [ ] Any patches that are no longer applied are deleted from the port's
directory.
- [x] The version database is fixed by rerunning `./vcpkg x-add-version
--all` and committing the result.
- [x] Only one version is added to each modified port's versions file.
Usage test pass with following triplets:
```
x86-windows
x64-linux
x64-windows
x64-windows-static
```
