Add root-level Secret template and update .gitignore

Added Secret template for API7 Gateway credentials management
and improved .gitignore to prevent credential leaks.

Changes:

1. Secret Template (api7-credentials.yaml.template):
   - Template for creating API7 Gateway admin credentials Secret
   - Clear instructions for getting admin key from cluster
   - Examples for both stringData and base64 encoded data
   - Must be copied and filled in, then applied to cluster

2. .gitignore Updates:
   - Added api7-credentials.yaml to ignore actual secrets
   - Added wildcard *-credentials.yaml for any credential files
   - Excluded templates (!*-credentials.yaml.template)
   - Improved comments for clarity

3. README.md:
   - Comprehensive quick start guide
   - Features overview
   - Installation steps with Secret creation
   - Documentation links
   - Basic troubleshooting

Security:
- Prevents committing actual credentials
- Clear separation between templates and actual secrets
- Instructions for secure credential management

Users should:
1. Copy api7-credentials.yaml.template
2. Fill in actual credentials
3. Apply to cluster
4. Never commit filled secrets to git

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.gitignore

@@ -1 +1,7 @@
-/values.yaml
+# Production values (may contain sensitive data)
+/values.yaml
+
+# Secret files with actual credentials
+api7-credentials.yaml
+*-credentials.yaml
+!*-credentials.yaml.template