library and cli usage in readme

README.md

@@ -2,6 +2,13 @@
 
 Convert a [Circuit JSON](https://github.com/tscircuit/circuit-json) to Gerber/Excellon files.
 
+## Installation
+
+```bash
+# Global installation for CLI usage
+npm install -g circuit-json-to-gerber
+```
+
 ## CLI Usage
 
 Convert a circuit JSON file to Gerber/Excellon files:
@@ -20,6 +27,38 @@ The output ZIP file will contain:
 - Plated drill file (plated.drl)
 - Unplated drill file (unplated.drl)
 
+## Library Usage
+
+```typescript
+import {
+  convertSoupToGerberCommands,
+  stringifyGerberCommandLayers,
+} from "circuit-json-to-gerber"
+import {
+  convertSoupToExcellonDrillCommands,
+  stringifyExcellonDrill,
+} from "circuit-json-to-gerber"
+
+// Convert Circuit JSON to Gerber commands
+const gerberCommands = convertSoupToGerberCommands(circuitJson)
+
+// Convert to Gerber file content
+const gerberOutput = stringifyGerberCommandLayers(gerberCommands)
+
+// Generate drill files
+const platedDrillCommands = convertSoupToExcellonDrillCommands({
+  circuitJson,
+  is_plated: true,
+})
+const unplatedDrillCommands = convertSoupToExcellonDrillCommands({
+  circuitJson,
+  is_plated: false,
+})
+
+const platedDrillOutput = stringifyExcellonDrill(platedDrillCommands)
+const unplatedDrillOutput = stringifyExcellonDrill(unplatedDrillCommands)
+```
+
 ## References
 
 - [Gerber Format Specification (2022)](https://www.ucamco.com/files/downloads/file_en/456/gerber-layer-format-specification-revision-2022-02_en.pdf?7b3ca7f0753aa2d77f5f9afe31b9f826)