Update testimonia documentation

[wlpotter]

It looks like the documentation for testimonia is outdated, see https://github.com/srophe/caesarea-data/wiki/TEI-Encoding-Manual-for-A-Collection-of-Testimonia-for-Caesarea-Maritima#components-of-the-xml-description-of-the-testimonium

Should update with the TEI elements used.

Should also mark the use of CTS-URNs as deprecated and inconsistently implemented.

[wlpotter]

Also:

• [ ] section about the context note /body/desc[@type="context]
• [ ] add that we are marking line breaks (in editions of the text) with a tei:lb (cf. #100)

[wlpotter]

I can make the above two edits to documentation. If time, i will read through documentation again to see if there are other updates that are needed.