docs: replace placeholder install commands with real repo references

[netrajpatel]

Summary

• Filled in the <this-repo> placeholder across the Claude Code, Gemini CLI, and skills CLI install snippets so every command in the README is directly copy-pasteable (contentstack/contentstack-agent-skills shorthand where supported, full https://github.com/... URL for Gemini CLI, which requires it).
• Expanded the skills CLI section from one example to four: whole-bundle install, single-skill shorthand (@<skill-slug>), single-skill via full URL + --skill flag, and multi-skill install via repeated --skill flags — all verified by running them live against this repo (read-only --list mode).
• Delinked the "skills CLI" bullet from github.com/anthropics/skills — that repo documents the SKILL.md file format, not this CLI's command syntax, so the link was pointing readers at the wrong project.

Test plan

• Ran npx skills add contentstack/contentstack-agent-skills --list — confirmed shorthand resolves and lists all 21 skills
• Ran the @<skill-slug> and --skill flag forms against the real repo — confirmed they parse without error
• Confirmed --list mode performs no local writes (no changes to ~/.claude/skills or ~/.agents/skills)
• Manual visual check of rendered README on GitHub

🤖 Generated with Claude Code

[github-actions]

🔒 Security Scan Results

ℹ️ Note: Only vulnerabilities with available fixes (upgrades or patches) are counted toward thresholds.

Check Type	Count (with fixes)	Without fixes	Threshold	Result
🔴 Critical Severity	0	0	10	✅ Passed
🟠 High Severity	0	0	25	✅ Passed
🟡 Medium Severity	0	0	500	✅ Passed
🔵 Low Severity	0	0	1000	✅ Passed

⏱️ SLA Breach Summary

✅ No SLA breaches detected. All vulnerabilities are within acceptable time thresholds.

Severity	Breaches (with fixes)	Breaches (no fixes)	SLA Threshold (with/no fixes)	Status
🔴 Critical	0	0	15 / 30 days	✅ Passed
🟠 High	0	0	30 / 120 days	✅ Passed
🟡 Medium	0	0	90 / 365 days	✅ Passed
🔵 Low	0	0	180 / 365 days	✅ Passed

✅ BUILD PASSED - All security checks passed

[aniket-shikhare-cstk]

LGTM

[github-actions]

🔒 Security Scan Results

ℹ️ Note: Only vulnerabilities with available fixes (upgrades or patches) are counted toward thresholds.

Check Type	Count (with fixes)	Without fixes	Threshold	Result
🔴 Critical Severity	0	0	10	✅ Passed
🟠 High Severity	0	0	25	✅ Passed
🟡 Medium Severity	0	0	500	✅ Passed
🔵 Low Severity	0	0	1000	✅ Passed

⏱️ SLA Breach Summary

✅ No SLA breaches detected. All vulnerabilities are within acceptable time thresholds.

Severity	Breaches (with fixes)	Breaches (no fixes)	SLA Threshold (with/no fixes)	Status
🔴 Critical	0	0	15 / 30 days	✅ Passed
🟠 High	0	0	30 / 120 days	✅ Passed
🟡 Medium	0	0	90 / 365 days	✅ Passed
🔵 Low	0	0	180 / 365 days	✅ Passed

✅ BUILD PASSED - All security checks passed

[timbenniks-contentstack]

Thanks @netrajpatel, and for being the first to replace those <this-repo> placeholders! Your change is now part of #21, the combined 0.2.0 release PR. The install section there builds on it with real commands for every tool, and your example for installing several skills with one command made it into the README. You're credited in the PR description and as co-author on the commit. Closing in favour of #21.