Add a glossary of Stellar/remittance terms to the docs

[Codex723]

Summary

Add a glossary (anchor, escrow, path payment, memo, base fee, etc.) so contributors unfamiliar with Stellar can ramp up faster.

Difficulty

Good First Issue — estimated effort: ~1-3 hours. Labels: documentation, good-first-issue, good-first-issue

Where to Work

• See relevant files referenced in the description above.

How to Approach This

1. Keep new docs in Markdown, consistent with the existing README.md / FOUNDATION.md tone (concise, contributor-facing).
2. Cross-link from README.md (or CONTRIBUTING.md if it exists by the time you pick this up) so the new doc is discoverable.
3. Prefer concrete examples/commands over abstract descriptions wherever possible.
4. Have someone unfamiliar with that part of the codebase skim it before opening a PR, if possible — docs issues are judged on clarity, not length.

Acceptance Criteria

• New/updated doc file added at a sensible path and linked from README.md.
• Content is accurate against the current state of the code (not the stale FOUNDATION.md framing).
• Reviewed for clarity by someone other than the author, if possible.
• Code snippets/commands in the doc were actually run and confirmed to work.

Notes for Contributors

Comment on this issue before starting so it can be assigned to you and duplicate work is avoided. If the described approach doesn't quite fit once you're in the code (e.g. the file has moved, or there's a cleaner way to do it), that's fine — leave a comment explaining the deviation in your PR description rather than silently changing scope.