Readme: fix link to GNU Arm Embedded toolchain.

Author: flit

README.md

@@ -199,7 +199,7 @@ Recommended GDB and IDE setup
 -----------------------------
 
 The recommended toolchain for embedded Arm Cortex-M development is [GNU Arm
-Embedded](https://developer.arm.com/tools-and-software/open-source-software/gnu-toolchain/gnu-rm),
+Embedded](https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-rm),
 provided by Arm. GDB is included with this toolchain.
 
 For [Visual Studio Code](https://code.visualstudio.com), the