Add comprehensive deparse documentation to README Usage section

- Add deparse(parseTree: ParseResult): Promise<string> async function documentation
- Add deparseSync(parseTree: ParseResult): string sync function documentation
- Include proper TypeScript examples with ParseResult type usage
- Add import { ParseResult } from '@pgsql/types' type import as requested
- Complete API documentation now covers parsing and deparsing functionality

Co-Authored-By: Dan Lynch <[email protected]>

Author: devin-ai-integration[bot]

README.md

@@ -89,6 +89,32 @@ import { parsePlPgSQLSync } from 'libpg-query';
 const result = parsePlPgSQLSync(functionSql);
 ```
 
+### `deparse(parseTree: ParseResult): Promise<string>`
+
+Converts a parse tree back to SQL string. Returns a Promise for the SQL string.
+
+```typescript
+import { parseQuery, deparse } from 'libpg-query';
+import { ParseResult } from '@pgsql/types';
+
+const parseTree = await parseQuery('SELECT * FROM users WHERE active = true');
+const sql = await deparse(parseTree[0]);
+// Returns: string - reconstructed SQL query
+```
+
+### `deparseSync(parseTree: ParseResult): string`
+
+Synchronous version that converts a parse tree back to SQL string directly.
+
+```typescript
+import { parseQuerySync, deparseSync } from 'libpg-query';
+import { ParseResult } from '@pgsql/types';
+
+const parseTree = parseQuerySync('SELECT * FROM users WHERE active = true');
+const sql = deparseSync(parseTree[0]);
+// Returns: string - reconstructed SQL query
+```
+
 ### Type Definitions
 
 ```typescript