Update README.md

Author: ScottPJones

README.md

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+
+Unicode_Entities.jl: Support for using Unicode entity names for characters
+====================================================================
+
+This builds tables for looking up Unicode entity names and returning the Unicode character(s),
+looking up a character or pair of characters and finding Unicode entity names that return it/them,
+and finding all of the Unicode name completions for a particular string, if any.