[docs] add BSD 3-Clause License
[docs] add BSD 3-Clause License

cornell-brg/pymtl,cfelton/pymtl,jck/pymtl,Glyfina-Fernando/pymtl,tj93/pymtl,12yujim/pymtl,Glyfina-Fernando/pymtl,tj93/pymtl,jck/pymtl,tj93/pymtl,Glyfina-Fernando/pymtl,cornell-brg/pymtl,jck/pymtl,cfelton/pymtl,cornell-brg/pymtl,jjffryan/pymtl,jjffryan/pymtl,cfelton/pymtl,12yujim/pymtl,jjffryan/pymtl,12yujim/pymtl