docs: add staying updated section to help and README

Promote /gsd:whats-new and update command visibility.
GSD evolves fast — users should check periodically.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

README.md

@@ -77,6 +77,20 @@ npx get-shit-done-cc
 
 That's it. Verify with `/gsd:help` inside your Claude Code interface.
 
+### Staying Updated
+
+GSD evolves fast. Check for updates periodically:
+
+```
+/gsd:whats-new
+```
+
+Update with:
+
+```bash
+npx get-shit-done-cc@latest
+```
+
 <details>
 <summary><strong>Non-interactive Install (Docker, CI, Scripts)</strong></summary>
 

commands/gsd/help.md

@@ -26,6 +26,20 @@ Output ONLY the reference content below. Do NOT add:
 3. `/gsd:plan-phase <number>` - Create detailed plan for first phase
 4. `/gsd:execute-plan <path>` - Execute the plan
 
+## Staying Updated
+
+GSD evolves fast. Check for updates periodically:
+
+```
+/gsd:whats-new
+```
+
+Shows what changed since your installed version. Update with:
+
+```bash
+npx get-shit-done-cc@latest
+```
+
 ## Core Workflow
 
 ```