Update language in project-tools index

[sjspielman]

We'd like to update some of the language in https://github.com/AlexsLemonade/OpenScPCA-analysis/blob/reproducibility-docs/docs/getting-started/project-tools/index.md.

• Say more plainly that renv and conda are for installing packages in modules (among other things for conda, but don't get into the weeds)
• Mention nextflow and docker as good to know but not strictly required.

We'll do this towards the end of the #487 epic.

[sjspielman]

Closed by #600