Add a bunch of: "SPDX-License-Identifier: GPL-2.0-only" comments.

examples/alignment.rem

@@ -1,6 +1,7 @@
 # Demo the columns() function
 #
 # Run as:  remind -@2 alignment.rem
+# SPDX-License-Identifier: GPL-2.0-only
 
 SET $AddBlankLines 0
 BANNER %

examples/ansitext

@@ -2,6 +2,7 @@
 #
 # A little demo script that displays ANSI text attributes
 # Not all attributes work on all terminals... your mileage may vary.
+# SPDX-License-Identifier: GPL-2.0-only
 
 remind -@2 - <<'EOF'
 

examples/astro

@@ -3,6 +3,7 @@
 # A little demo script that displays astronomical events
 #
 # Best used in a UTF-8 environment.
+# SPDX-License-Identifier: GPL-2.0-only
 
 # Set this variable to 1 if your terminal has a dark background or 0 if
 # it: light.

examples/defs.rem

@@ -17,6 +17,7 @@
 # 									    #
 # This file is part of REMIND.						    #
 # Copyright (C) 1992-2022 Dianne Skoll                                      #
+# SPDX-License-Identifier: GPL-2.0-only
 # 									    #
 #############################################################################