add doc files

README.rst

adaptive/__init__.py

adaptive/learner/average_learner.py

adaptive/learner/balancing_learner.py

adaptive/learner/base_learner.py

adaptive/learner/data_saver.py

adaptive/learner/integrator_learner.py

adaptive/learner/learner1D.py

adaptive/learner/learner2D.py

adaptive/learner/learnerND.py

adaptive/learner/triangulation.py

adaptive/notebook_integration.py

adaptive/runner.py

docs/Makefile

docs/environment.yml

docs/source/conf.py

docs/source/implemented-algorithms.rst

docs/source/index.md

docs/source/index.rst

docs/source/reference/adaptive.learner.average_learner.rst