Update README.md

README.md

@@ -6,4 +6,4 @@ To run this code:
 To annotate images:
 * Arrows are used to change images.
 * Clicking adds annotations.
-* S saves annotations as  `.mat` file and  `.txt` file. NOTE: previously saved files will be overwritten.
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+* S saves annotations as a `.mat` file and a `.txt` file. NOTE: previously saved files will be overwritten.
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