Add librosa reference.

audio/paddleaudio/features/core.py

@@ -11,6 +11,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+# Modified from librosa(https://github.com/librosa/librosa)
 import warnings
 from typing import List
 from typing import Optional

docs/source/reference.md

@@ -31,3 +31,7 @@ We borrowed a lot of code from these repos to build `model` and `engine`, thank
 * [chainer](https://github.com/chainer/chainer/blob/master/LICENSE)
 - MIT License
 - Updater, Trainer and more utils.
+
+* [librosa](https://github.com/librosa/librosa/blob/main/LICENSE.md)
+- ISC License
+- Audio feature