small suggestion

[tjdodson]

I updated the install instructions because they were inaccurate for qmake

additionally I received some error for cmake

❯ cmake cmake -G Ninja .. -DCMAKE_PREFIX_PATH="/opt/homebrew/Cellar/qt@5/5.15.17;/opt/homebrew"
CMake Warning:
  Ignoring extra path from command line:

   "/Users/trevordodson/apm_planner/build/cmake"


CMake Error at /opt/homebrew/lib/cmake/Qt5Core/Qt5CoreConfig.cmake:14 (message):
  The imported target "Qt5::Core" references the file

     "/opt/homebrew/.//mkspecs/macx-clang"

  but this file does not exist.  Possible reasons include:

  * The file was deleted, renamed, or moved to another location.

  * An install or uninstall procedure did not complete successfully.

  * The installation package was faulty and contained

     "/opt/homebrew/lib/cmake/Qt5Core/Qt5CoreConfigExtras.cmake"

  but not all the files it references.

Call Stack (most recent call first):
  /opt/homebrew/lib/cmake/Qt5Core/Qt5CoreConfigExtras.cmake:57 (_qt5_Core_check_file_exists)
  /opt/homebrew/lib/cmake/Qt5Core/Qt5CoreConfig.cmake:227 (include)
  /opt/homebrew/lib/cmake/Qt5Gui/Qt5GuiConfig.cmake:93 (find_package)
  /opt/homebrew/lib/cmake/Qt5Widgets/Qt5WidgetsConfig.cmake:93 (find_package)
  /opt/homebrew/lib/cmake/Qt5/Qt5Config.cmake:28 (find_package)
  CMakeLists.txt:12 (find_package)


-- Configuring incomplete, errors occurred!

I wasn't able to figure out what the issue was.

[billbonney]

If you update the commit message to be something like below i.e. more descriptive than "small suggestion" I'll merge 👍

Update README.md to fix macOS build instructions

- also fixes formatting to be 'better'