Add new maintainers

Author: Hoverbear

src/doc/rustc/src/platform-support/riscv64gc-unknown-linux-gnu.md

@@ -7,8 +7,9 @@ RISC-V targets using the *RV64I* base instruction set with the *G* collection of
 
 ## Target maintainers
 
--  TODO
-
+- Kito Cheng, <kito.cheng@gmail.com>, https://github.com/kito-cheng
+- Michael Maitland, <michaeltmaitland@gmail.com>, https://github.com/michaelmaitland
+- Robin Randhawa, <robin.randhawa@sifive.com>, https://github.com/robin-randhawa-sifive
 
 ## Requirements