readme updated with qutip.devmajor and cupy instructions

[MrRobot2211]

This updates the readme with an step by step explanation of how to install the unreleased version and required libraries, Just for adventurers.

See #14. About usage, maybe we should point to the data_layer documentation. In any case there is not much usage we can reap from it now, but I have a basic notebook with examples already is there a correct place to hang it?

[coveralls]

Pull Request Test Coverage Report for Build 1006562432

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
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• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-1.9%) to 82.432%

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Files with Coverage Reduction	New Missed Lines	%
src/qutip_cupy/init.py	2	89.47%

Totals
Change from base Build 1003702665:	-1.9%
Covered Lines:	61
Relevant Lines:	74

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💛 - Coveralls

[nwlambert]

For what its worth, this worked without much fuss in windows 👍

[nwlambert]

maybe this needs a git+ prefix?

[MrRobot2211]

Good catch