Make changes to license identifiers + documentation update

Author: jessbryte

data/license_url_to_identifier_mapping.csv

@@ -5,7 +5,7 @@
 "https://creativecommons.org/licenses/by-nc-sa/4.0","CC BY-NC-SA 4.0"
 "https://creativecommons.org/licenses/by-nd/4.0","CC BY-ND 4.0"
 "https://creativecommons.org/licenses/by-sa/4.0","CC BY-SA 4.0"
-"https://creativecommons.org/publicdomain/certification/1.0/us","CC PUBLIC DOMAIN 1.0 US"
+"https://creativecommons.org/publicdomain/certification/1.0/us","CC CERTIFICATION 1.0 US"
 "https://creativecommons.org/publicdomain/mark/1.0","PDM 1.0"
 "https://creativecommons.org/publicdomain/zero/1.0","CC0 1.0"
 "https://creativecommons.org/licenses/by/3.0","CC BY 3.0"
@@ -649,6 +649,6 @@
 "https://creativecommons.org/licenses/nd-nc/1.0/nl","CC ND-NC 1.0 NL"
 "https://creativecommons.org/licenses/sa/1.0/nl","CC SA 1.0 NL"
 "https://creativecommons.org/licenses/nc-sampling+/1.0/tw","CC NC-SAMPLING+ 1.0 TW"
-"https://creativecommons.org/licenses/sampling/1.0/tw","CC CERTIFICATION 1.0 US
+"https://creativecommons.org/licenses/sampling/1.0/tw", "CC SAMPLING 1.0 TW"
 "https://creativecommons.org/licenses/sampling+/1.0/tw","CC SAMPLING+ 1.0 TW"
-"https://creativecommons.org/licenses/publicdomain","CC PUBLICDOMAIN"
+"https://creativecommons.org/licenses/publicdomain","CC CERTIFICATION 1.0 US"

sources.md

@@ -195,4 +195,4 @@ The Internet Archive is a nonprofit digital library offering free access to mill
 - In summary, it queries licenseurl and language fields for all items containing "creativecommons.org" in their metadata
 - Aggregated counts are saved to CSV files for licenses and languages.
 - License normalization uses a canonical mapping defined in `license_url_to_identifier_mapping.csv`.
-- Language normalization using Babel and [iso-639](https://github.com/jacksonllee/iso639), see also [iso-639 standards](https://www.loc.gov/standards/iso639-2/), you can also checkout [iso639-2](https://www.loc.gov/standards/iso639-2/php/English_list.php)
+- Language normalization using Babel and [iso-639](https://pypi.org/project/iso639-lang/) see [github information](https://github.com/jacksonllee/iso639), see also [iso-639 standards](https://www.loc.gov/standards/iso639-2/), you can also checkout [iso639-2](https://www.loc.gov/standards/iso639-2/php/English_list.php)