Add citation information (#15)

- Add citation information (009fc64090ef773e9c65aca7b0fb9bdf33f14eca)

README.md

@@ -176,7 +176,9 @@ Within the PMC Open Access Subset, there are three groupings based on available
 
 ### Citation Information
 
-[More Information Needed]
+```
+PMC Open Access Subset [Internet]. Bethesda (MD): National Library of Medicine. 2003 - [cited YEAR MONTH DAY]. Available from https://www.ncbi.nlm.nih.gov/pmc/tools/openftlist/
+```
 
 ### Contributions
 

open_access.py

@@ -22,15 +22,8 @@ import datasets
 from datasets.tasks import LanguageModeling
 
 
-# TODO: Add BibTeX citation
-# Find for instance the citation on arxiv or on the dataset repo/website
 _CITATION = """\
-@InProceedings{huggingface:dataset,
-title = {A great new dataset},
-author={huggingface, Inc.
-},
-year={2020}
-}
+PMC Open Access Subset [Internet]. Bethesda (MD): National Library of Medicine. 2003 - [cited YEAR MONTH DAY]. Available from https://www.ncbi.nlm.nih.gov/pmc/tools/openftlist/
 """
 
 _DESCRIPTION = """\
@@ -46,8 +39,12 @@ The PMC Open Access Subset is one part of the PMC Article Datasets
 
 _HOMEPAGE = "https://www.ncbi.nlm.nih.gov/pmc/tools/openftlist/"
 
-# TODO: Add the licence for the dataset here if you can find it
-_LICENSE = ""
+_LICENSE = """\
+Within the PMC Open Access Subset, there are three groupings based on available license terms:
+- Commercial Use Allowed - CC0, CC BY, CC BY-SA, CC BY-ND licenses;
+- Non-Commercial Use Only - CC BY-NC, CC BY-NC-SA, CC BY-NC-ND licenses; and
+- Other - no machine-readable Creative Commons license, no license, or a custom license.
+"""
 
 _URL = "https://ftp.ncbi.nlm.nih.gov/pub/pmc/oa_bulk/{subset}/txt/"
 _SUBSETS = {