Fixed client port issues in 'run.sh'

[Cc-a23187]

thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', examples/gg18_keygen_client.rs:269:55
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

1. This is rust reporting an error when I run the run.sh file . I found that the port number in the running parameters of gg18_keygen_client and gg18_sign_client was different from the port number run by gg18_sm_manager, so I changed it to 8000 before the program executes correctly.
2. Update README.md "Run GG18 Demo ->Sign" shell default port from "8001" to "8000".