Change installation method

[stiefn]

Change the installation instructions in the README

For some obscure reason, cargo build works, while cargo install throws an error on the same codebase.

[MrToph]

it's because cargo install ignores the Cargo.lock by default.

This worked for me and should be the "official" command IMO:

cargo install --path . --locked

[stiefn]

it's because cargo install ignores the Cargo.lock by default.

This worked for me and should be the "official" command IMO:

cargo install --path . --locked

Awesome, this works. Thanks for your input!

[ritzdorf]

Thanks @MrToph