Added note about quotation restriction.

README

@@ -43,6 +43,7 @@ Bugs/Todo
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 * (cue/toc) Line numbers in error messages are off sometimes.
+* (cue/toc) Strings cannot be quoted with single quotes.
 * (toc) Binary CD-TEXT data is parsed, but not saved.
 * (toc) Only a single data file is supported.
 * (cueprint) Allow specifying zero padding for numbers.