fixup! Improve wording of paragraph

Signed-off-by: Carmen Bianca BAKKER <[email protected]>

Author: carmenbianca

spec.md

@@ -148,7 +148,7 @@ An example of a comment header:
 
 If these tags are additionally used in the file without describing the file's
 actual license or copyright (for example: as part of an output command or
-documentation), these occurrences MAY be put between two comments:
+documentation), these occurrences SHOULD be put between two comments:
 `REUSE-IgnoreStart` and `REUSE-IgnoreEnd`. The REUSE Tool then ignores all
 Copyright and Licensing Information between these comments. This technique MUST
 NOT be used to ignore valid Copyright and Licensing Information.