add cmake example

[XxChang]

Please see README.md for details

Thanks

[haixuanTao]

Thanks!

Would it be possible to add it to the github action ci.yml as follows:

      - name: "Cmake example"
        timeout-minutes: 30
        run: cargo run --example cmake-dataflow

[XxChang]

This example only works on Linux right now. I don't have chance to fix it on Windows and MacOS, also I'm not good at Windows and MacOS. So I only check it on Linux by adding if: runner.os == 'Linux'

Sorry about that.

[haixuanTao]

Looks good to me. @phil-opp , could you have a quick look, as i don't have that much experience in CMake. Thanks!

[phil-opp]

I don't have much cmake experience either, but I think this looks all reasonable. Thanks for the contribution!

[haixuanTao]

Thanks @phil-opp , guess we´ll both learn this way :)