suggestion for lag docs

[cyrush]

use a yaml file instead of a json in the docs

much simpler + cleaner.

https://alpine-dav.readthedocs.io/en/latest/lagrangian.html

[cyrush]

Gunther asked me about yaml details, and I wanted to share here as well.

You can now use an actions.yaml instead of an actions.json.

We added YAML a while back, since YAML is much easier for humans to craft.

We have several YAML actions examples in our docs:

https://ascent.readthedocs.io/en/latest/Actions/Examples.html

And a few in the cloverleaf tutorial:

https://github.com/Alpine-DAV/ascent/tree/develop/src/examples/tutorial/cloverleaf_demos

Another relevant change, you no longer need to finish with:

action: execute
action: reset