MAINTAINERS: add entry for the pin-init crate

Add maintainers entry for the `pin-init` crate.

This crate is already being maintained by me, but until now there
existed two different versions: the version inside of the kernel tree
and a user-space version at [1]. The previous patches synchronized these
two versions to reduce the maintenance burden. In order to keep them
synchronized from now on, separate the maintenance from other Rust code.

Link: https://github.com/Rust-for-Linux/pin-init [1]
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Link: https://lore.kernel.org/r/20250308110339.2997091-23-benno.lossin@proton.me
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: y86-dev

MAINTAINERS

@@ -20737,6 +20737,19 @@ T:	git https://github.com/Rust-for-Linux/linux.git alloc-next
 F:	rust/kernel/alloc.rs
 F:	rust/kernel/alloc/
 
+RUST [PIN-INIT]
+M:	Benno Lossin <benno.lossin@proton.me>
+L:	rust-for-linux@vger.kernel.org
+S:	Maintained
+W:	https://rust-for-linux.com/pin-init
+B:	https://github.com/Rust-for-Linux/pin-init/issues
+C:	zulip://rust-for-linux.zulipchat.com
+P:	rust/pin-init/CONTRIBUTING.md
+T:	git https://github.com/Rust-for-Linux/linux.git pin-init-next
+F:	rust/kernel/init.rs
+F:	rust/pin-init/
+K:	\bpin-init\b|pin_init\b|PinInit
+
 RXRPC SOCKETS (AF_RXRPC)
 M:	David Howells <dhowells@redhat.com>
 M:	Marc Dionne <marc.dionne@auristor.com>