Make tags modal text configurable

[alexandermendes]

A quick change to make the text below configurable, as with the other modals:

The tags added below will help researchers locate items of particular interest by being used to generate keywords that can be searched via the Browse page.

For programmatic research purposes the data will also be available via the API at https://annotations.libcrowds.com/annotations/playbills-item-tags/

Tags can be added by anyone but, once confirmed, can only be deleted by administrators. If you have spotted a tag that you think is incorrect or should be removed for any reason please contact digitalresearch@bl.uk.

By default, a new tag will be added for each word. To create tags that comprise multiple words please follow the convention of adding a hyphen between words (e.g. my-long-tag).