docs: clarify compass priority is set automatically (#27393)

Fixes Algora bounty: #19970

This PR was AI-assisted (Claude Code) and reviewed by a human
before submission.

Co-authored-by: pcminh <pham.cao.minh@talentnet.vn>

Author: pmjnt

docs/en/config/compass.md

@@ -203,6 +203,7 @@ These are prefixed with [CAL*MAGx*](../advanced_config/parameter_reference.md#CA
 - [CAL_MAGn_ROT](../advanced_config/parameter_reference.md#CAL_MAG0_ROT) can be used to determine which compasses are internal.
   A compass is internal if `CAL_MAGn_ROT==1`.
 - [CAL_MAGx_PRIO](../advanced_config/parameter_reference.md#CAL_MAG0_PRIO) sets the relative compass priority and can be used to disable a compass.
+  Priority is assigned automatically during calibration (external compasses are preferred over internal ones), so manual configuration is not normally required.
 
 ## Debugging