added tox file

tox.ini

+[tox]
+envlist = py310
+
+[flake8]
+max-line-length = 120
+
+[testenv]
+deps =
+    coverage
+    flake8
+    mypy
+    black
+    -r requirements.txt
+
+commands =
+    coverage erase
+    coverage run --source neurons_client -m pytest neurons_client/ test/
+    coverage xml
+    coverage html
+    coverage report --fail-under 80
+    black --check .
+    flake8 neurons_client/ test/
+    mypy neurons_client
+    sphinx-build -b html docs/source docs/build