add section in README about limitations

[oakmac]

We should add a section to the README about the limitations of this project.

Similar to:

• https://github.com/clj-kondo/clj-kondo?tab=readme-ov-file#macros

[oakmac]

We should mention that this tool is intended for "code at rest" more than "code in flight". ie: final product vs editing experience

There are things that you may do while editing code that you probably should clean up before it lands on master.

[oakmac]

There may some valid ns forms that this tool does not support (like Issue #38).