docs: add sample skill

.opencode/skills/sample-skill/SKILL.md

@@ -0,0 +1,31 @@
+---
+name: sample-skill
+description: Use when the user says sample skill, skill demo, or asks how an opencode SKILL.md should be structured; demonstrates a tiny project-local skill with practical assistant workflow guidance.
+---
+
+# Sample Skill
+
+This is a minimal project-local opencode skill. It exists as a reference for how a skill is structured and as a tiny reusable workflow the assistant can load when the user asks for a skill example.
+
+## When To Use
+
+- Use when the user asks for a sample skill or skill template.
+- Use when demonstrating the required `SKILL.md` frontmatter and body format.
+- Do not use for unrelated coding tasks just because a skill exists.
+
+## Workflow
+
+- Confirm the specific outcome the user wants if the request is ambiguous.
+- Inspect the relevant files before changing anything.
+- Make the smallest correct change.
+- Verify the result with a focused read, typecheck, test, or other lightweight check when available.
+- Summarize the changed files and any required restart or reload step.
+
+## Example Response Style
+
+When this skill is relevant, keep responses direct and actionable:
+
+```text
+I created a project-local skill at .opencode/skills/sample-skill/SKILL.md.
+Restart opencode for the new skill to be discovered by future sessions.
+```