Update "What can be expected from alchemical simulations?" section

[fjclark]

Proposed Change

Update "What can be expected from alchemical simulations?" section.

• Possibly shorten further by moving material to the "multiple calculations" paper (although I have already moved over most of the material)
• Add a walkthrough of a “dummy calculation” (which could be a particular realisation of a general workflow laid out in Figure 1 - see Make Figure 1 the "central axis" of the paper #133)? This will lead on to discussion of particular methods.

Proposed Authors and Reviewers

Please confirm (before the end of January) that you are happy to author/ review and state when you're available. Authors, please say roughly when you plan to contribute the changes (no later than the end of May).

Proposed author: @ppxasjsm (already confirmed via Overleaf)
Proposed reviewer: Volunteer wanted