doc: mention the test target qemu_mps2_an385_v6m

Author: yvt

README.md

@@ -132,5 +132,6 @@ In this case, you need to run `rustup target add thumbv7m-none-eabi`.
 ### How to Run Tests
 
  - Hosted platform and target-independent tests: `cargo test --all`
- - The Arm-M port and NUCLEO-F401RE: `cargo run -p constance_port_arm_m_test_runner -- -t nucleo_f401re`
- - The Arm-M port and Arm MPS2+ AN385 (QEMU emulation): `cargo run -p constance_port_arm_m_test_runner -- -t qemu_mps2_an385`
+ - The Armv7-M port and NUCLEO-F401RE: `cargo run -p constance_port_arm_m_test_runner -- -t nucleo_f401re`
+ - The Armv7-M port and Arm MPS2+ AN385 (QEMU emulation): `cargo run -p constance_port_arm_m_test_runner -- -t qemu_mps2_an385`
+ - The Armv6-M port and Arm MPS2+ AN385 (QEMU emulation): `cargo run -p constance_port_arm_m_test_runner -- -t qemu_mps2_an385_v6m`