Add ZecMap guide

[cybercraftsolutionsllc]

Addresses #1653.

Summary

• Adds site/Using_Zcash/zecmap.md as the requested ZecMap wiki page.
• Covers what ZecMap is, how it helps users find ZEC-accepting businesses, listing submission and verification flow, contributor profiles, rewards program notes, future roadmap items, and safe-use tips.
• Includes links to ZecMap, Zcash usage docs, and ZecHub Wiki.

Validation

• Markdown-only documentation change.
• Verified the requested target path did not already contain zecmap.md before submission.
• Checked recent/open PR metadata for obvious ZecMap duplicates before opening this PR.

Notes

This is submitted for the 0.2 ZEC ZecMap wiki page bounty in #1653.