Fix docstring indentation in SiliconStep.submit

The docstring had improperly indented options list that caused Sphinx
RST parsing errors in CI (but not locally). Added blank line after the
summary and proper indentation for the options block.

Error: "Unexpected indentation" at line 3 of submit docstring

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: robtaylor

chipflow_lib/platform/silicon_step.py

@@ -108,10 +108,11 @@ def prepare(self):
 
     def submit(self, rtlil_path, args):
         """Submit the design to the ChipFlow cloud builder.
+
         Options:
-          --dry-run: Don't actually submit
-          --wait: Wait until build has completed. Use '-v' to increase level of verbosity
-          --log-file <file>: Log full debug output to file
+            --dry-run: Don't actually submit
+            --wait: Wait until build has completed. Use '-v' to increase level of verbosity
+            --log-file <file>: Log full debug output to file
         """
         if not args.dry_run:
             # Check for CHIPFLOW_API_KEY_SECRET or CHIPFLOW_API_KEY