Add summary guidance about quotation marks

[julian-cable]

Add guidance:
When indicating the start or end of a direct quote, use curly quotation marks. In all other contexts, such as when writing code samples, code syntax, hexadecimal numbers, or hypertext links, use straight quotation marks.

Refer to "Typographical Considerations" topic in IBM Style:
https://www.ibm.com/docs/en/ibm-style?topic=punctuation-quotation-marks#typographical-considerations

[julian-cable]

Added guidance to Punctuation.xml.