docs: clean up whitespace and fix typo in tutorial.md

[daynual]

Clean up trailing whitespace and fix grammatical typo in tutorial.md.

[daynual]

Successfully builds and generates code:

❯ ./scripts/generate_code.py

warning:
  cannot generate code directly from .proto files

Fields in struct ProtoMessage have gap between ids
Fields in struct OtherMessage have gap between ids
When you use --proto, that you should check for conformity yourself, using the existing --conform/home/dan/flatbuffers/flatc:
warning:
  /home/dan/flatbuffers/tests/rust_namer_test.fbs:26: 8: warning: field names should be lowercase snake_case, got: Message

I get the same warning building on main branch. Looks unrelated to these changes.

Originally I intended to create this PR just for bb268bf, but saw a bunch of trailing whitespace. I can drop that commit if requested.