add example crates in workspace.members

[choleraehyq]

add example crates into workspace members, or they cannot be by cargo build built directly. Error msg:

error: current package believes it's in a workspace when it's not:
current:   /Users/x/dynasm-rs/doc/examples/hello-world/Cargo.toml
workspace: /Users/x/dynasm-rs/Cargo.toml

this may be fixable by adding `doc/examples/hello-world` to the `workspace.members` array of the manifest located at: /Users/x/dynasm-rs/Cargo.toml
Alternatively, to keep it out of the workspace, add the package to the `workspace.exclude` array, or add an empty `[workspace]` table to the package's manifest.

[choleraehyq]

@CensoredUsername please take a look, thanks.

[CensoredUsername]

Thanks!