DOC: fix formatting + language issues in write_select_yaml.rst

[NickleDave]

didn't clean this up in #119 https://github.com/NickleDave/hybrid-vocal-classifier/blob/main/docs/source/howto/write_yaml/writing_select_yaml.rst

still need to:

• [ ] fix rst formatting issues, e.g. use double-backticks instead of single backticks to get monoscript instead of italics
• [ ] revise language that talks about birdsong, make less specific, e.g. "vocalizations"