33 - pyside6

[mxochicale]

Addressing #33

Hi @thompson318

This PR seems to be ready to be reviewed and contains the following changes:

• updates tox python version, conda packages, & requirements
• updates for 01_Starting_Out.rst, including conda env; steps; and main readme python version
• updates packages version in 07_UserInterface; other minors for linting, ci and typos
• adds reference for Goals of Good Software Design at 04_Planning
• adds reference release cycle versions in 10_Publishing
• fix install_requirements in 09_Releasing

Thanks, Miguel