Minor modifications

README.md

@@ -129,7 +129,12 @@ The entries in the training sets have been ranked automatically by how
 likely they are paraphrases, best first, worst last. The quality
 parameter indicates the estimated proportion (in percent) of true
 paraphrases in the set. Allowed quality values range between 60 and
-100, in increments of 5 (60, 65, 70, ... 100).
+100, in increments of 5 (60, 65, 70, ..., 100). A value of 60 means
+that 60% of the sentence pairs in the downloaded set are estimated to
+be true paraphrases (and the remaining 40% are not). A higher value
+produces a smaller but cleaner set. The smaller sets are subsets of
+the larger sets, such that the `quality=95`set is a subset of
+`quality=90`, which is a subset of `quality=85`, and so on.
 
 
 ### Data Instances