Revise description of the head element https://bl.syriac.uk/documentation/guidelines#heading

[davidamichelson]

@wlpotter Would you want to add one more sentence describing how this was generated (does it list top level items only?, is there a numberic cut off for items?).

Thanks

https://bl.syriac.uk/documentation/guidelines#heading

[wlpotter]

Note cf. srophe/britishLibrary-data#573 for changes that we will implement to how the contents notes looks. I will update documentation to what we do currently, but we may want to leave this open or create a follow up issue to revise once we've updated the notes

[wlpotter]

I've made changes to the section but it may need additional revision

[wlpotter]

Left to do here:

• pointer to the subject classification section for full list of terms available from Wright's Taxonomy