Recommend dependency version management tooling based on use case

Similar to the problem in https://github.com/pypa/python-packaging-user-guide/issues/118 with regards to virtual environment management, our current tooling recommendations don't provide a pointer to higher level dependency version management tools like pipenv or pip-tools, they only refer to pip itself.

While we don't want to overwhelm people with choice, I think we're currently doing folks a disservice by letting them think pip is all there is, rather than guiding them towards more opinionated higher level tooling:

• pipenv: web application development (and potentially other forms of application development)
• pip-tools: general application development (useful when pipenv doesn't align with your needs)
• conda: language-independent cross-platform package (useful when you have extensive external dependencies)

Start by reading the current tooling recommendations and the related python-packaging-user-guide issue 118. Determine where pip is currently presented and update that documentation to guide readers toward pipenv, pip-tools, or conda based on their use case. Done means the recommendations are clear without overwhelming readers with unnecessary choices.