Set up Build continuous integration

We want to create a CI workflow called `compile` so that it builds the application in an Ubuntu environment with the command:
`g++ -std=c++17 -o tally main.cpp`

It should be triggered to run whenever:
- a pull request has been made for the **main** branch,
- any new commits have been pushed to a branch called `devops`

We also want to integrate a status badge of the **compile** workflow into `README.md` so we can quickly see the latest result.