Update LICENSE with full Apache-2.0 text

[BigBlueHat]

The Apache-2.0 license is applied by putting the full text of the license into LICENSE and putting the header text (which is currently in the LICENSE file) into each code file's top comment area--per https://www.apache.org/legal/apply-license.html#new

This at least starts that fix. 😁

This should also help robots properly tag this repo as Apache-2.0 licensed.

❤️ 🎩

[VirginiaBalseiro]

Thank you for this! We'll merge it soon and make the other required accompanying changes along with it :)

[csarven]

Heya @BigBlueHat / Benjamin, thanks for doing this. Meant to write back to you soon after we saw this PR but totally got distracted while working on something else. Held off because we wanted to also get those related changes in at the same time.