Acknowledge TiDB upstream in README

Add an Acknowledgments section calling out that Marino is a hard fork
of pingcap/parser and thanking the TiDB team and upstream contributors.

Author: claude

README.md

@@ -12,6 +12,13 @@ The goal of this project is to build a Golang parser that is fully compatible wi
 - Extensible: adding a new syntax requires only a few lines of Yacc and Golang code changes.
 - Good performance: the parser is generated by goyacc in a bottom-up approach. It is efficient to build an AST tree with a state machine.
 
+## Acknowledgments
+
+Marino is a hard fork of [pingcap/parser](https://github.com/pingcap/parser),
+the MySQL-compatible SQL parser developed as part of [TiDB](https://github.com/pingcap/tidb).
+Huge thanks to the TiDB team and all the upstream contributors whose work this
+project is built on.
+
 ## License
 
 Marino is under the Apache 2.0 license. See the LICENSE file for details.