README: Add documentation on build instructions for users

Some users may not be comfortable using a pre-compiled binary from brew or the Releases Page. They would prefer to build the binary themselves for more confidence in mcpjungle.

We should add proper build instructions in the docs so that they can build mcpjungle on their own infra or local machines.

Notes:

1. We should provide instructions on how to build using both goreleaser and docker
2. Take care to also supply the right version info during build process so that the final binary has appropriate output when running mcpjungle version