Add license information

[vazhnov]

Hello!

Could you please add information about the license of this repository — is it allowed to copy, change and use the code in any purpose?
It would be great to see any popular open source license here.

[dmccomas]

OpenSatKIt combines three products each with their own licenses plus the code I've written (cFS apps, ruby scripts, etc.). Here's a license summary:

COSMOS: Ball modified GNU Affero General
Public License, version 3

cFS: A combination of Apache 2.0 and NASA Open Source agreement

42: NASA Open Source agreement

My Code: Copyleft GNU General Public License (GPL)

[vazhnov]

Could you please add this information into README.md?