Update README.md

Author: juliohm

README.md

@@ -4,9 +4,11 @@
 
 This package is intended for developers of data transforms such as
 the maintainers of [TableTransforms.jl](https://github.com/JuliaML/TableTransforms.jl).
+It defines a simple API and basic transforms that work with any type of object such as
+the `Identity` and `Sequential` transforms.
 
 [build-img]: https://img.shields.io/github/workflow/status/JuliaML/TransformsBase.jl/CI
 [build-url]: https://github.com/JuliaML/TransformsBase.jl/actions
 
 [codecov-img]: https://codecov.io/gh/JuliaML/TransformsBase.jl/branch/master/graph/badge.svg
-[codecov-url]: https://codecov.io/gh/JuliaML/TransformsBase.jl
+[codecov-url]: https://codecov.io/gh/JuliaML/TransformsBase.jl