23.40.4: missing additional new requirement on clang from documentation

[tgurr]

Expected behavior

Do not fail to build / have correct documentation about required dependencies.

[...]
error: failed to run custom build command for `mtu v0.2.9`
Caused by:
  process didn't exit successfully: `/var/tmp/paludis/build/net-analyzer-openvas-scanner-23.40.4/work/openvas-scanner-23.40.4/rust/target/release/build/mtu-2c7d9b352e02a147/build-script-build` (exit status: 101)
  --- stdout
  cargo:rustc-check-cfg=cfg(bsd)
  cargo:rerun-if-env-changed=TARGET
  cargo:rerun-if-env-changed=BINDGEN_EXTRA_CLANG_ARGS_aarch64-unknown-linux-gnu
  cargo:rerun-if-env-changed=BINDGEN_EXTRA_CLANG_ARGS_aarch64_unknown_linux_gnu
  cargo:rerun-if-env-changed=BINDGEN_EXTRA_CLANG_ARGS
  --- stderr
  thread 'main' (1322648) panicked at /var/tmp/paludis/build/net-analyzer-openvas-scanner-23.40.4/work/ecargo-vendor/bindgen/lib.rs:622:31:
  Unable to find libclang: "couldn't find any valid shared libraries matching: ['libclang.so', 'libclang-*.so', 'libclang.so.*', 'libclang-*.so.*'], set the `LIBCLANG_PATH` environment variable to a path where one of these files can be found (invalid: [])"
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
warning: build failed, waiting for other jobs to finish...

(Ideally building openvas-scanner wouldn't require yet another additional compiler.)

Actual behavior

237e3ae added clang to the docker file but missed it when making changes to the rust/README.md.

Steps to reproduce

1. do not have clang installed
2. try to build the rust code cargo build --release

GVM versions

gsa: -

gvm: -

openvas: -

gvm-libs: -

openvas-smb: -

ospd-openvas: -

Environment

Operating system: Exherbo Linux

Installation method / source: source based distribution / packages

Logfiles

https://gitlab.exherbo.org/tgurr/net/-/jobs/198859#L1963