Add README for API

api/README.md

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+# API
+
+Tomo has a small number of built-in functions and bunch of types.
+
+## Types
+
+- [Arrays](arrays.md)
+- [Booleans](booleans.md)
+- [Channels](channels.md)
+- [Integers](integers.md)
+- [Floating point numbers](nums.md)
+- [Integer Ranges](ranges.md)
+- [Sets](sets.md)
+- [Tables](tables.md)
+- [Text](text.md)
+- [Threads](threads.md)
+
+## Built-in Functions
+
+### `say`
+
+**Description:**  
+Prints a message to the console.
+
+**Usage:**  
+```markdown
+say(text:Text) -> Void
+```
+
+**Parameters:**
+
+- `text`: The text to print.
+
+**Returns:**  
+Nothing.
+
+**Example:**  
+```markdown
+say("Hello world!")
+```
+
+---
+
+### `fail`
+
+**Description:**  
+Prints a message to the console, aborts the program, and prints a stack trace.
+
+**Usage:**  
+```markdown
+fail(message:Text) -> Abort
+```
+
+**Parameters:**
+
+- `message`: The error message to print.
+
+**Returns:**  
+Nothing, aborts the program.
+
+**Example:**  
+```markdown
+fail("Oh no!")
+```
+
+---