Feat: make the library available as a swift package

[MojtabaHs]

By merging this PR, people will be able to import SmoothRoundedRectangle after adding the repository as a dependency.

Note: Please remember to tag a version for the project so it can be added using the standard dependency format like:

dependencies: [
    .package(url: "https://github.com/sachinkmr57/SmoothRoundedRectangle", from: "1.0.0"),
]

For your convenience, you can use the following commands to tag a version, but feel free to use any version number you prefer:

git tag 1.0.0
git push origin --tags