Bug reports (including wishlist items) can be submitted to RT.
Test cases written using Test::More are always appreciated.
If something doesn't work as documented, or causes unexpected crashes, and you know how to fix it, then either attach a patch to the bug report (see above) or as a pull request to the project on GitHub.
Please try to follow the coding style used in the rest of the project. (Tab indents, spaces for alignment, British English spellings, pod at the end of code but the start of test cases, etc.)
Adding Test Cases
New test cases for the Type::Tiny test suite are always welcome. The coveralls page for Type::Tiny should reveal what parts of the code are most needing good test cases. Any files with below 95% coverage are highest priority.
Type::Tiny is now also on Codecov which does coverage accounting slightly differently, giving some stricter targets to aim for.
I'm not really a C programmer, nor am I that familiar with Perl's internals, so help with Type::Tiny::XS is always appreciated. There are some type constraints in Types::Standard, Types::Common::String, and Types::Common::Numeric which don't have XS implementations, and none of Types::TypeTiny has an XS implementation. (Given that the last module is used internally by Type::Tiny a lot, an XS implementation of that could provide a good speed boost!)
Writing Type Libraries
Though I'm unlikely to bundle many more type libraries in this distribution, uploading your own type libraries to CPAN will strengthen the Type::Tiny ecosystem.
You've reached the end of the manual!
But each class, type library, and other package includes more detailed documentation.