update srtool build instructions

These changes come from the runtime-801 branch and were not merged into master, leading to people not knowing that they were using a more recent version of the runtime. This is linked to #195 (closed). I'm merging this until we improve the branching strategy.

docs/dev/verify-runtime-code.md

@@ -2,14 +2,18 @@
 
 When voting for a runtime upgrade, you should check that the proposed hash actually corresponds to the published code you reviewed. Otherwise, a malicious runtime upgrade could be advertised as a legitimate one.
 
-```docker
+```sh
+mkdir runtime/gdev/target
+chmod o+w runtime/gdev/target
+# Workaround see !239
+echo -e "[toolchain]\nchannel = \"1.74.0\"\ncomponents = [ \"rust-std\", \"rust-src\" ]" > runtime/gdev/rust-toolchain.toml
 docker run \
   -i \
   --rm \
   -e PACKAGE=gdev-runtime \
   -e RUNTIME_DIR=runtime/gdev \
   -v $PWD:/build \
-  paritytech/srtool:1.60.0 build --app --json -cM
+  paritytech/srtool:1.74.0-0.13.0 build --app --json -cM
 ```
 
 Then, the runtime wasm bytecode is generated in this location:
@@ -19,5 +23,6 @@ runtime/gdev/target/srtool/release/wbuild/gdev-runtime/gdev_runtime.compact.comp
 ```
 
 To compare it to last official :
+
 - download it here : https://git.duniter.org/nodes/rust/duniter-v2s/-/releases
 - compare `sha256sum` of it and of the one you've built