This PR removes the references to initializing Git submodules as part of
building Zed.
These are no longer needed, as our only submodule was removed in #11672.
Release Notes:
- N/A
Just adding a short note about `cargo build --release` and the location
of the compiled binary. It helps a lot to streamline usage of Zed day to
day on Linux.
Release Notes:
- N/A
