added readthedocs.yml for documentation builder

readthedocs.yml

+version: 2
+
+build:
+  os: "ubuntu-22.04"
+  tools:
+    python: "3.9"
+
+# python:
+  # install:
+    # - requirements: mbtrack2.yml
+
+sphinx:
+  configuration: docs/source/conf.py
+
+formats:
+  - pdf
+  - epub
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