This commit (with approval from all contributors) dual licenses
the torch-mlir project under both the standard LLVM license and the
standard PyTorch license. This will facilitate moving code between
torch-mlir and the two upstream projects.
The standard file comment is now:
```
// This file is licensed under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// Also available under a BSD-style license. See LICENSE.
```
See `LICENSE` in the project root for the terms of both licenses.
* Updates the LICENSE to the same verbiage as used in the circt project.
* Adds the incubator disclaimer to the README.
* Reworks the introduction of the README to more accurately reflect the eventual scope.
* There is a fair amount of further rework of the repo that needs to take place. This is just the minimal cosmetic changes now that it is part of LLVM.