Add MySQL to the Database section.

README.md

@@ -239,6 +239,7 @@ Databases and data stores with C APIs.
   [``BSD-3-Clause``][BSD-3-Clause]
 * [libmongoc][233] - High-performance client library for [MongoDB][234]. [``Apache-2.0``][Apache-2.0]
 * [LMDB][105] - Ultra-fast, ultra-compact key-value embedded data store. [``OLDAP-2.8``][OLDAP-2.8]
+* [MySQL][551] - The world's most popular open source database. [``GPL-2.0-only``][GPL-2.0-only]
 * [PostgreSQL][121] - Powerful object-relational database system. [``PostgreSQL``][PostgreSQL]
 * [Redis][51] - Advanced key-value store. [``BSD-3-Clause``][BSD-3-Clause]
 * [sophia][244] - Modern, embeddable key-value database.
@@ -1643,3 +1644,4 @@ support for C.
 [548]: https://github.com/libarchive/libarchive
 [549]: https://github.com/LiamBindle/MQTT-C
 [550]: https://github.com/LeoVen/C-Macro-Collections
+[551]: https://github.com/mysql/mysql-server