Add sniffing and developing notes

Add sniffing and developing notes

docs/Develop.md

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+# Developing
+To start developing and contributing, install in dev mode.
+
+`pipenv install --dev`
+
+Review the [How It Works](How_It_Works.md) doc to understand the basics and then dive into the code.
+
+As features and functions are added, be sure to add tests to keep the test coverage high.
+
+# Testing
+Bumper uses pytest for the majority of test cases, review current tests in the /tests directory.
+
+### Running tests
+Enter pipenv shell `pipenv shell`
+
+**Run tests**
+
+- `python -m pytest tests`
+
+
+**Run tests with coverage**
+
+- `python -m pytest --cov=./ tests`
+
+**Run tests with coverage html report**
+
+- `python -m pytest --cov=./ tests --cov-report html:tests/report`
+    - The report will be output into tests/report/index.html for further analysis.