Add pip installation instructions

[brycemines]

This draft starts rewriting the README file to make it more user-friendly. This PR is still a draft, so please let me know if you have any changes or additions.

The changes I have made so far include:

• adding a setup section with instructions for pip installing
• add a usage section with examples copied from the paper
• update the examples instructions for installing from pypi
• update the development instructions for clarity and consistency

Other changes needed:

• update the readme inside notebooks to use the pypi instructions
• update the documentation sphinx page to use the pypi instructions

closes #217, #204

[brycemines]

One question I have for @castelao and @biavillasboas is if I should include the examples in the readme?

I mostly copied the examples from the paper, which I like. But for the repo, I don't like that these examples will not run. Moreover, I did not think of a way to make a working example without adding a lot more lines of code to create and save test bathymetry and current files.

[castelao]

@brycemines , thanks for doing this. I've been thinking about improving this README, but I haven't managed to find the time yet. I was thinking of unloading some content here. We now have public documentation. I think there is the documentation is the place to extend on details, but here should be just brief enough for someone trying to create an opinion if it is worth investing time to learn more about our library or not. For instance, we shall mention development guidance here, but all the development information should be in a 'developers' section in the documentation.

What do you think about that? If you agree with that direction, you don't need to address everything in a single PR, but I suggest small steps, different PRs, so we can work with the time we have and secure small but constant progress.

[brycemines]

I agree with all of your comments, @castelao. I undid some changes I was not sure about and instead focused on adding the point that mantaray can be installed with pip. I will create an issue for everything else.