Refine tutorial roadmap references

Tutorial/phase-16-linux-boot-contract/phase-16.md

@@ -28,6 +28,9 @@ wrong, Linux often just hangs early with little output.
 
 - Read the RISC-V Linux boot protocol and list required register state.
 - Draft a device tree matching your memory map and interrupt topology.
+- Use the modern CPU ISA properties: `riscv,isa-base = "rv32i"` and
+  `riscv,isa-extensions = "i", "m", "a", "zicsr", "zifencei"`. Keep the legacy
+  `riscv,isa = "rv32ima_zicsr_zifencei"` string only as a compatibility fallback.
 - Decide whether the first Linux attempt uses direct M-mode or OpenSBI.
 
 ## Pitfalls
@@ -47,4 +50,3 @@ wrong, Linux often just hangs early with little output.
 - RISC-V Linux boot protocol: https://docs.kernel.org/arch/riscv/boot.html
 - RISC-V device-tree CPU bindings: https://www.kernel.org/doc/Documentation/devicetree/bindings/riscv/cpus.yaml
 - OpenSBI: https://github.com/riscv-software-src/opensbi
-