If you want to contribute to deconst-client, please consider contributing to Kitematic first! Whenever possible, I'd prefer to see Kitematic get better and better, and periodically merge relevant changes from upstream, rather than diverge.
If you do want to contribute something deconst-client specific, welcome and thank you! The Kitematic contributing guide has some handy pointers on development prequisites and development environment setup that you should read.
By contributing your code, you agree to license your contribution under the Apache license.