Legal pedantry: not strictly every file needs an SPDX header

FossilOrigin-Name: 26ae286925b712e56e0b01c00e3dfd4744381a495490b00795fc7a890db65d62

Author: danshearer

LICENCES/README.md

@@ -2,8 +2,7 @@
 
 This directory documents the licences applying to the LumoSQL project.
 
-All files in this project should in addition have a [Software Package Data Exchange](https://spdx.dev)
-machine-readable header. 
+All significant files in this project should in addition have a [Software Package Data Exchange](https://spdx.dev) machine-readable header. 
 
 # MIT Licence