Update README.md

README.md

@@ -127,6 +127,7 @@ Made of 6 subsets:
 1. **large** contains 25,000 hours of read / spontaneous and clean / noisy transcribed speech.
 2. **medium** contains 2,500 hours of read / spontaneous and clean / noisy transcribed speech.
 3. **small** contains 250 hours of read / spontaneous and clean / noisy transcribed speech.
+4. **clean** contains 13,000 hours of read / spontaneous transcribed speech. YODA and People's Speech data are excluded from this subset as, despite data curation, some errors remain in the transcriptions.
 5. **dev** contains 15 hours (more details in the next section).
 6. **test** contains 21 hours (more details in the next section).