Clarify how to update the in-person logistics page

[sjspielman]

This PR makes a few updates that hopefully clarify how to update in-person logistics for a given workshop:

• The issue template itself now provides more context for while file to modify and why
• The relevant markdown files now contain guiding comments at the top instructing how to update contents

Let me know if this is helpful, or if other instructions would be more helpful!

[Jen-OMalley]

Super helpful! 🚀