Wiki: Some improvements to Development Workflow Wiki

[htrivedi04]

I was following the Development Workflow Wiki page as I'm new to contributing to this project. It is a good source of knowledge for newbies. However, I found some outdated / misleading information in the Development Workflow Wiki page, which can be fixed easily -

• In the Set up Git - Clone SymPy section - The download size of SymPy should now be 88.5MB instead of 77MB.
• In the Setup Virtual Environments section - The conda create -n sympy-dev-py27 python=2.7 mpmath should also ideally include numpy package.
• In the Be sure that all tests pass section - A little info on what 's', 'f' and 'w' signify in the test case results would be good for new contributors.

I can fix these if you approve of these, although I might need some information about the last point. Let me know what suits you best.

[asmeurer]

Feel free to edit the wiki.

Note that numpy is only required for a very small subset of SymPy (lambdify basically). But it should be clear there that you should add whatever other packages you need, like ipython, jupyter, matplotlib, and so on. Or you can install them in the environment after you activate it with conda install jupyter and so on.

Regarding the tests, s means the test is skipped (you can see the reason using --verbose. F means the test failed. f means the test failed, but it was expected to fail (XFAIL). wmeans the test was skipped because it is too slow (it can be run with--slow). X` means the test was expected to fail (XFAIL), but it passed.