add Plano agent skills framework and rule set (#797)

* feat: add initial documentation for Plano Agent Skills

* feat: readme with examples

* feat: add detailed skills documentation and examples for Plano

---------

Co-authored-by: Adil Hafeez <adil.hafeez@gmail.com>

skills/rules/_template.md

@@ -0,0 +1,26 @@
+---
+title: Rule Title Here
+impact: MEDIUM
+impactDescription: Optional one-line description of the impact
+tags: tag1, tag2, tag3
+---
+
+## Rule Title Here
+
+Brief explanation of what this rule is and why it matters for Plano developers and agents.
+
+**Incorrect (explain what's wrong):**
+
+```yaml
+# Bad config or CLI example
+```
+
+**Correct (explain what's right):**
+
+```yaml
+# Good config or CLI example
+```
+
+Optional explanatory text elaborating on the principle or listing key points.
+
+Reference: https://github.com/katanemo/archgw