Add the `LICENSE.md` file from OM.jl

[DilumAluthge]

This PR adds the LICENSE.md file from the https://github.com/JKRT/OM.jl/pull/37 branch.

Fixes #61

[CLAassistant]

All committers have signed the CLA.

[DilumAluthge]

cc: @JKRT @viralbshah

[JKRT]

@casella I think this should be OK s.t we can register OMJulia; the package is a wrapper around omc. This would also close the following ticket https://github.com/OpenModelica/OMJulia.jl/issues/61

(Also tagging Adrian @adrpo )

What do you think?

[ViralBShah]

This will also allow us to register the package in the Julia General registry, making it easy for others to download and use.

[casella]

LGTM. The only missing point is explaining that only half of OSMC-PL is OSI approved, i.e. GPL v3

[casella]

@DilumAluthge I'm sorry but I messed up. This is not the right license, you need the runtime OSMC-PL-RT license instead. I'll take care of that ASAP.