Feedback: Check installation requirements

[evilrobot-01]

Feedback received:

Small nit in the documentation: cargo install doesn't work if you don't have nightly as default (or add +nightly)

It might be especially useful to get this checked via CI so we detect any regressions once resolved.

[weezy20]

Add instructions for building from source?

cargo build --release && cp ./target/release/pop /usr/local/bin

[evilrobot-01]

Tried installing from rust Docker image, required the installation of cmake only and then pop installed fine. rust:slim required cmake build-essential libssl-dev pkg-config curl but then also worked fine.

Seems this was resolved by #73 so closing.