adds USB storage module tutorial

[Frijol]

Adds tutorial for USB mass storage module.

Still needs:

• Example
• GIF of example's results
• Description of results for Step 4
• Bonus problem

[johnnyman727]

We should remove step 3 - that's only a BLE command.

Also, we should tell people where the flash storage was mounted:

var fs = require('fs');
var path = require('path');
var mountPoint = '/mnt/sda1';

fs.readFile(path.join(mountPoint, 'myFile.txt'), function(err, contents) {
  ...
});

The first flash drive you plug in will be mounted at /mnt/sda1 and the second will be mounted at /mnt/sdb1.

We may also want to note this corner case?

[Frijol]

mountPount > mountPoint I think in your code above?

[johnnyman727]

Yes, thanks.

[Frijol]

anyone is welcome to review, @johnnyman727 you can be on point for it if no one else wants to

[johnnyman727]

looks great to me!