Added SPDX license identifier to the src/shared/WETH9.sol file and added `--no-commit` flag to the forge install command in the README.md file

[SyedAsadKazmi]

1. Added SPDX license identifier to the src/shared/WETH9.sol file to silence this warning:

   Warning: SPDX license identifier not provided in source file. Before publishing, consider adding a comment containing "SPDX-License-Identifier: " to each source file. Use "SPDX-License-Identifier: UNLICENSED" for non-open-source code. Please see https://spdx.org for more information. --> @chainlink/local/src/shared/WETH9.sol

2. Added --no-commit flag to the forge install command in the README.md file, so as to avoid this error while executing the command:

   Error: The target directory is a part of or on its own an already initialized git repository, and it requires clean working and staging areas, including no untracked files.

   Check the current git repository's status with git status. Then, you can track files with git add ... and then commit them with git commit, ignore them in the .gitignore file, or run this command again with the --no-commit flag.

[andrejrakic]

Thank you for your PR, @SyedAsadKazmi! However, we can't merge it.

Regarding the SPDX-License-Identifier warning, I understand it's annoying, but since the original WETH9 contract doesn't have that line, we can't add it. For reference, take a look at this https://github.com/smartcontractkit/ccip/blob/ccip-develop/contracts/src/v0.8/ccip/test/WETH9.sol

As for the --no-commit flag, we discussed this internally and decided to follow Foundry's official documentation for installing dependencies rather than forcing the use of this flag. Same as OpenZeppelin for example https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/README.md#foundry-git

[SyedAsadKazmi]

Noted, @andrejrakic. I totally understand that.

Can you please shed some light on how to install chainlink-local (or any other dependency) without the --no-commit flag?

Thanks.