This commit makes the production of the pdf file contingent upon
whether or not 'compare_centres' is enabled in
'reproduce/analysis/config/analyse-plot-params.conf'. The default
remains 'YES', but 'NO' (or anything different to 'YES') should
disable the option.

A comment is added to 'README.md' to clarify that the default
that we will retain in the official version 2 commit will aim to
reproduce the submitted version 2, but that we recommend that
users who do not feel the need for Table 4 and the final
paragraph in Section 4.2 should disable 'compare_centres'.
We leave the calculation times to those for the disabled
state of compare_centres.

This commit also adds the timing estimate for a 256^3 simulation
in README.md, warning the user that this is very unwise with
the current state of the full pipeline.

Full testing of switching between the YES and NO states is best
done with a `./project make clean-analyse-conf` step in between.

This works for me.