docs: contributor-facing documentation cleanup (typos + stale links)

[Devansh-567]

Summary

Full pass over the contributor-facing docs (root README, CONTRIBUTING, docs/, docs/v1/, rust/) to fix typos and stale/incorrect links encountered while onboarding to the build, release, codegen, Rust, Python, and Bazel workflows. No behavioral, code, or protobuf changes, text only.

What changed

Typos

• resepectively → respectively (docs/README.md, docs/v1/README.md)
• apparrent → apparent (docs/v1/README.md)
• navgiate → navigate (rust/README.md)
• postive → positive (docs/v1/guidance-for-generating-p4info.md)
• mssages → messages (docs/v1/p4runtime-id-notes.md)
• duplicated word "to to dockerhub" → "to dockerhub" (docs/tools/README.md)
• stray backtick in `p4lang/p4rt-asciidoc:latest` Docker` image → `p4lang/p4rt-asciidoc:latest` Docker image (docs/v1/README.md)

Capitalization / naming consistency

• Github → GitHub everywhere it appears as the product name (README.md, docs/README.md, CONTRIBUTING.md)

Stale / outdated links

• README.md: the three "Guidelines for using Protocol Buffers" links pointed at developers.google.com/protocol buffers/docs/..., which has been superseded by protobuf.dev. Updated to:
  • https://protobuf.dev/overview/#updating-defs
  • https://protobuf.dev/programming-guides/proto3/#updating
  • https://protobuf.dev/programming-guides/proto3/#backward
• docs/README.md: the "latest working draft" spec link pointed at https://p4.org/p4runtime/spec/main/P4Runtime-Spec.html, which doesn't resolve. Replaced with the actual GitHub Pages URL already used elsewhere in the repo: https://p4lang.github.io/p4runtime/spec/main/P4Runtime-Spec.html.
• docs/v1/README.md: the P4.org specifications page link pointed at https://p4.org/specs, which has moved to https://p4.org/specifications/.

Files changed

• README.md
• CONTRIBUTING.md
• docs/README.md
• docs/tools/README.md
• docs/v1/README.md
• docs/v1/guidance-for-generating-p4info.md
• docs/v1/p4runtime-id-notes.md
• rust/README.md

Why this shape

This started from a couple of visible typos but turned into a full pass because contributor docs are one of the first things new contributors read before touching build/release/codegen/Rust/Python/Bazel workflows, small inconsistencies (broken links, "Github" vs "GitHub", duplicated words) add up and erode trust in the docs. Kept strictly to wording/links; no changes to .proto files, generated code, or CI.

Testing

• Manually re-read every changed file end-to-end.
• Grepped the full doc tree for the fixed typo strings and for Github (mis-capitalized) to confirm no other occurrences remain.
• Verified the replacement URLs (protobuf.dev pages, GitHub Pages spec URL, p4.org specifications page) resolve to the intended content.

Not included (follow-up candidates, kept out to stay reviewable)

• docs/tools/README.md also says "push the image to dockerhub" could be restyled to "Docker Hub" for consistency, left as-is since it's a style choice, not a typo.
• No changes to py/README.md (it is a symlink to the root README.md, so there's nothing to edit there independently).

[jafingerhut]

LGTM