doc: add dev part "verify runtime code"

docs/dev/verify-runtime-code.md

+# Compile the runtime with srtool
+
+```docker
+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
+```
+
+Then, the runtime wasm bytecode is generated in this location:
+
+```
+runtime/gdev/target/srtool/release/wbuild/gdev-runtime/gdev_runtime.compact.compressed.wasm
+```