docs: document the R/Z run/crouch toggles for text mode

[dmccoystephenson]

Summary

Addresses #480 (run/crouch don't work in text mode). On investigation, the toggle model the issue proposed already exists: run_toggle (R) and crouch_toggle (Z) are bound to terminal-usable ASCII keys, toggle the player's run/crouch with a single press, show the state in the status bar ("Run: ON/OFF", "Crouch: ON/OFF"), and leave the pygame held Shift/Ctrl behavior unchanged (worldScreen.py:962-978, keyBindings.py:25-26). All of the issue's acceptance criteria are met by existing code.

The remaining gap was discoverability: the README controls table listed only the held Shift/Ctrl bindings, not the R/Z toggles — and since a terminal can't detect held keys, the toggles are the only way to run/crouch in --text mode. This PR documents them.

Changes

• Controls table: Shift (hold) or R (toggle) | Run and Ctrl (hold) or Z (toggle) | Crouch.
• New tip: in text/terminal mode, use R/Z instead of holding Shift/Ctrl; the active state shows in the status bar.

Test plan

• Docs-only (README + CHANGELOG); no code changed, so the test suite is unaffected.
• Verified against source that R/Z toggles exist, are ASCII (terminal-usable), set status, and don't conflict with other bindings.

Closes #480

🤖 Generated with Claude Code

[dmccoystephenson]

Self-review rubric (reviewed by Claude; CI green on head):

• Scope: PASS — README.md + CHANGELOG.md only; both serve text mode: run and crouch don't work (held-key state unavailable) #480's discoverability gap.
• Tests-new / Tests-fix: N/A — docs-only, no code changed (anchor UNVERIFIED-not-applicable; pytest unaffected, CI green regardless).
• Docs accuracy: PASS — R/Z verified as the actual run_toggle/crouch_toggle bindings (keyBindings.py:25-26) with status output (worldScreen.py:962-978); table now matches code.
• Issue resolution: PASS — text mode: run and crouch don't work (held-key state unavailable) #480's intent (run/crouch usable in text mode + discoverable) is satisfied; the toggle feature already existed, this documents it. Reasoning stated in the PR body for auditability.
• Markdown fences: PASS — no triple-backtick blocks added.
• No do-not-auto-merge path: PASS — README/CHANGELOG only.