improve schema

models/SiaN/_schema.md

@@ -1,4 +1,8 @@
-# _schema.md
+# SiaN Schema
+
+Notebook structure definition for SiaN model.
+
+---
 
 ## Format
 
@@ -10,14 +14,18 @@
 # markdown
 """Description"""
 
-# inline:
-<custom code>
+# shell:
+<shell commands>
 ```
 
 ## Directives
 
-- `# code:` - include file from src/
-- `# markdown` - description block
-- `# inline:` - custom code cell
+| Directive      | Description                        |
+|----------------|------------------------------------|
+| `# code:`      | Include file from src/             |
+| `# markdown`   | Description block                  |
+| `# shell:`     | Shell script cell                  |
+
+---
 
 `build.py` generates notebook from `_schema.py`.