Add Workspace Based Development to the Upcoming Bevy Book.

## How can Bevy's documentation be improved?

This issue is my submitting the idea of adding a workspace based workflow guide to the upcoming bevy book. Based on personal experience and those who have reached out to me I think this would be valuable.

If there is interest I would volunteer to write the section.

The section would roughly contain/recomend:
- Games start out as a single crate with a strong focus on bevy plugin hygiene.
- When compile times get annoying, then you break the game out into workspace crates along the lines of bevy plugins.
- General advice on how to handle Components or resources that may be used across plugins in a workspace based workflow.
- How to architect the workspace crates so maximal parallel compilation is achieved.

Start by reviewing the upcoming Bevy Book's existing structure and identify where a workspace-based development guide belongs. The finished section should cover plugin hygiene, when to split a game into workspace crates, sharing components and resources, and structuring crates for parallel compilation.

Written by the indexing model from the issue text.