Adding support for colcon-cd

[hegde-atri]

Currently colcon-cd seems to be missing (colcon-cd is a shell function for colcon-core to change current working directory).

Looking at pkgs/colcon/argcomplete.nix I made an effort to create a pkgs/colcon/cd.nix, but don't know how to proceed as pypi - (0.1.1) has an outdated version compared to their github - (0.2.1).

If I could get some guidance on how to proceed and if there's anything else I need to do apart from just adding this package.

(It's my first time contributing to this repository so forgive me if there's anything I've done incorrectly; I will squash all my commits into one before its ready to merge :D)