Added Wikipedia to the documentation

Author: oree-xx

sources.md

@@ -174,3 +174,21 @@ adjust video parameters, and obtain search results.
   - API key required
   - Query limit: depends on the type and number of requests
   - Data available through JSON format
+
+## Wikipedia API
+
+**Description:** The Wikipedia API allows users to query statistics of pages,
+categories, revisions from a public API endpoint. We have included two urls in the project: The WIKIPEDIA_BASE_URL AND WIKIPEDIA_MATRIX_URL. The WIKIPEDIA_BASE_URL provides access to articles, categories, and metadata from the English version of Wikipedia.
+It runs on the MediaWiki Action API, but this instance only provides English Wikipedia data.
+Then the WIKIPEDIA_MATRIX_URL provides access to information of all wikimedia projects including the different language edition of wikipedia. It runs on the Meta-Wiki API.
+
+**API documentation link:**
+https://meta.wikimedia.org/w/api.php - Meta-Wiki
+https://www.mediawiki.org/wiki/API:Sitematrix
+https://en.wikipedia.org/w/api.php - English instance
+https://www.mediawiki.org/wiki/API:Main_page
+
+**API information:**
+  - No API key required
+  - Query limit: It is rate-limited only to prevent abuse
+  - Data available through XML or JSON format