Make this error message slightly more useful

Author: AngledLuffa

src/edu/stanford/nlp/parser/nndep/DependencyParser.java

@@ -648,7 +648,7 @@ private double[][] readEmbedFile(String embedFile, Map<String, Integer> embedID)
         log.info("Embedding File " + embedFile + ": #Words = " + nWords + ", dim = " + dim);
 
         if (dim != config.embeddingSize)
-            throw new IllegalArgumentException("The dimension of embedding file does not match config.embeddingSize");
+            throw new IllegalArgumentException("The dimension of embedding file does not match config.embeddingSize (" + dim + " vs " + config.embeddingSize + ").  Perhaps set the -embeddingSize flag");
 
         for (int i = 0; i < lines.size(); ++i) {
           splits = lines.get(i).split("\\s+");