Add LICENSE.md to specify the software license

[petrdvorak]

Currently, you write in the README.md file:

If these projects helped you save development time, you can support my work on Patreon or buy me a cup of coffee...

Well, we would of course love to do this, but the payment for a coffee does not cover the intellectual property transfer very well. Basically, with the current state of the repository (which contains a really nice code samples), anyone who takes an inspiration from your code is in unclear licensing position.

To fix this, I recommend using some well-known license, such as Apache 2.0, and add it to the repository, or - if you want to be a bit more protective of your IP - you can use some *GPL-based license.