doc: Added documentation for pytree

[samuelkuehnel]

Description

Added documentation about current status and technical aspects about decision tree.

Fixes #47

Type of change

Does this PR introduce a breaking change?

no

Most important changes

New documentation file

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works (might be obsolete with CI later on)
• New and existing unit tests pass locally with my changes (might be obsolete with CI later on)

[github-actions]

Simulation results

Metric	Value
Avg. driving score	0.008823
Avg. route completion	0.075
Avg. infraction penalty	0.274269
Collisions with pedestrians	0.274269
Collisions with vehicles	0.0
Collisions with layout	97.995
Red lights infractions	195.989
Stop sign infractions	0.0
Off-road infractions	0.0
Route deviations	0.006
Route timeouts	0.0
Agent blocked	195.989
Yield emergency vehicles infractions	0.0
Scenario timeouts	0.0
Min speed infractions	195.989
undefined	0.0

[JuliusMiller]

Nice documentation!