Add LICENSE

[jcheng5]

Hi there, I'd like to use your SimpleGraticule plugin, but I can't unless you attach a license to your project by putting a LICENSE file in your root directory.

If you don't have a strong opinion about what license to choose, you might consider using the one that Leaflet itself uses, the BSD 2-Clause (similar to MIT in that it's very simple and permissive):

https://github.com/Leaflet/Leaflet/blob/master/LICENSE

You'd just need to change the Copyright statements in the beginning to the appropriate name(s) and years.

Thank you for your consideration!

[ablakey]

Hi:

I've added a BSD license identical to what Leaflet uses. Thanks for making it so easy to do so with your succinct description of what to do.