Update why_public_domain.md

docs/why_public_domain.md

@@ -48,7 +48,7 @@ in the public domain:
   you have problems it's not my fault, but also please
   report bugs so I can fix them"--so dumb!
 
-4. discussion from stb_howto.txt on what YOU should do for YOUR libs
+4. full discussion from stb_howto.txt on what YOU should do for YOUR libs
 
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