Add passive tracers documentation

[wenrongcao]

I added a md file called "readpassivetracer.md" and two associated images under /docs/src to show how to initiate tracers, perform tracer selection, and read the information back to Julia. No LaMEM source code is changed. Changes only exit in the /docs.

[boriskaus]

That’s great - thanks a lot.

I have two requests:

1. Can you make a link to your document here ? That way a link to the page will appear in the side bar
2. can you add a copy of the full, working, script to the examples directory? It would allow interested users to directly run this

[wenrongcao]

Will do. For (2), I do not see examples. Only see notebooks and scripts. Do you want me to make a new examples directory? Also, files in notebooks and scripts should be better sorted/combined if they all belong to examples.

[boriskaus]

Sorry, I meant scripts which is where we have the other examples as well

[boriskaus]

And feel free to better sort the scripts in those directories

[boriskaus]

since you rearranged the files in the scripts directory, the tests now fail (we always run these examples as part of the test to ensure that they keep working once we update the code). Can you perhaps update the file https://github.com/JuliaGeodynamics/LaMEM.jl/blob/main/test/test_examples.jl
and while you are at it, you can also add your new example to the test.

[wenrongcao]

Ok, I see they are connected. Will fix these tomorrow.

[wenrongcao]

The Documentation check did not pass probably due to some (local?) path information related to Subduction3D.jl not being updated.

[boriskaus]

This is the error message:

ERROR: LoadError: Unable to generate remote link (local path does not exists)
 path: /home/runner/work/LaMEM.jl/LaMEM.jl/scripts/Subduction3D.jl

See here

The issue is in this line:

LaMEM.jl/docs/src/Subduction3D.md

Line 2 in 1c63624

EditURL = "../../scripts/Subduction3D.jl"