Document how to install PhotonLib of specific version (#1392)

docs/source/docs/programming/photonlib/adding-vendordep.rst

@@ -38,3 +38,9 @@ Add photonlibpy to `pyproject.toml`.
     ]
 
 See `The WPILib/RobotPy docs <https://docs.wpilib.org/en/stable/docs/software/python/pyproject_toml.html>`_ for more information on using `pyproject.toml.`
+
+Install Specific Version - Java/C++
+-----------------------------------
+In cases where you want to test a specific version of PhotonLib, make sure you have finished the steps in Online Install - Java/C++ and then manually change the version string in the photonlib vendordep json file(at ``/path/to/your/project/vendordep/photonlib.json``) to your desired version.
+
+.. image:: images/photonlib-vendordep-json.png