Add documentation

Firmware/Marlin_main.cpp

@@ -5816,6 +5816,12 @@ if(eSoundMode!=e_SOUND_MODE_SILENT)
 
     /*!
 	### M27 - Get SD status <a href="https://reprap.org/wiki/G-code#M27:_Report_SD_print_status">M27: Report SD print status</a>
+    #### Usage
+	
+	      M27 [ P ]
+	
+	#### Parameters
+	  - `P` - Show full SFN path instead of LFN only.
     */
     case 27:
       card.getStatus(code_seen('P'));