Update README and environment files

[leewujung]

This PR addresses #46:

• overhaul README
• create conda folder and host 2 version of environment files that use different echopype versions
• rename binder to .binder and create symbolic link to link to conda/environment.yml

[leewujung]

if we ourselves are providing/pointing at this official cloud platform (Binder) for users to test our examples out, then they 100% should run on this platform (and run well).

I agree, though this will put significant constraints on what is possible to show in the notebooks. From the guidelines:

Some code and some data. The code should take less than 10 minutes to run, and the data should be less than 10 MB. This might mean that you just pick one script from a bigger project, or bring a subset of your data. Note that it’s really important that the code and data can be made public because we’ll be using the public binder instance.

One way we can circumvent this is to show pull very minimal examples in Binder, and have bold text and let user know that they can change the amount of data by customizing the input file list.

I think we should stick with the original OOI notebook, but add the frequency-differencing there. For the hake notebook, the easiest is to limit the section used to only the portion where there is 1 region (out of however many in an EVR file), so that we can show the steps to do apply_mask and compute_NASC. I'll add these to the related issues.

Even with these though, the data will be larger than 10 MB, but we can give it a try.

There's also the backend problems with Binder

Yeah I didn't try to launch yesterday but I am seeing the same thing now. The previous version also did not work. I'll add an issue to investigate this.

[ctuguinay]

Oh just saw this. This looks good. I'm going to merge it now.