Adding y to install

[shimwell]

Description

Just worked through the install with @AlvaroCubi and he spotted some ideas for making the install a bit easier. This PR adds -y to the conda and mamba install instructions which saves the user having to enter Y to proceed

Fixes issue

Checklist

• [x] I'm making a PR from a feature branch on my fork into GEOUNED-org/GEOUNED/dev branch
• [ ] I have followed PEP8 style guide for Python or run a formatter such as black or ruff format on my code
• [x] I have made corresponding changes to the documentation
• [ ] I have added tests that prove my fix is effective or that my feature works

[shimwell]

this one is ready for review