docs: mark three more written files unsourceable

emulators/xenia-edge.yml

@@ -277,6 +277,7 @@ files:
 
   - name: "system/flash/"
     type: directory
+    unsourceable: "written by the emulator when it installs SystemUpdate_17559_USB.zip, no canonical file"
     path: "Xenia-Edge/system/flash/"
     standalone_path: "system/flash/"
     system: microsoft-xbox-360
@@ -290,6 +291,7 @@ files:
 
   - name: "system/sysext/"
     type: directory
+    unsourceable: "written by the emulator when it installs SystemUpdate_17559_USB.zip, no canonical file"
     path: "Xenia-Edge/system/sysext/"
     standalone_path: "system/sysext/"
     system: microsoft-xbox-360

emulators/xm6typeg.yml

@@ -276,6 +276,7 @@ files:
   # -- Battery-backed images, read at startup, written on exit when changed --
 
   - name: SRAM.DAT
+    unsourceable: "written by the emulator on exit, no canonical file"
     system: sharp-x68000
     required: false
     size: [16384, 65536]