docs: document registry-install & --fast-deps, fix node-install example

[mattmillerai]

ELI-5

If you told comfy-cli to install a node using its GitHub-style name
(ComfyUI-Impact-Pack), it failed with a confusing Node 'ComfyUI-Impact-Pack@unknown' not found error, because the command actually
wants the node's lowercase Comfy Registry ID (comfyui-impact-pack). Also,
comfy-cli has two different install commands (install and registry-install)
and a --fast-deps speed flag that were never explained. This PR is docs-only:
it explains all of that in the README so nobody hits the same wall.

What changed

Documentation only (README.md) — no code changes.

1. Node-install casing note — added a note under the comfy node install
   example clarifying the argument is the node's lowercase Comfy Registry ID,
   not the GitHub repo name, and that the wrong casing produces the
   Node '...@unknown' not found error from the issue.
2. install vs registry-install — new section explaining that install
   delegates to ComfyUI-Manager's cm-cli (multi-node, channel/mode-aware,
   supports the dependency flags, needs the Manager) while registry-install
   downloads a single published node straight from the Comfy Registry API and
   runs its bundled install script (no Manager required — the command the
   Registry's own instructions use).
3. --fast-deps — new section documenting what it does, the commands that
   accept it (comfy install, comfy node install, comfy node reinstall),
   and why registry-install does not (it bypasses comfy-cli's dependency
   resolver entirely).

Acceptance criteria

• README node-install example corrected to a working command — the literal
  example was already lowercase on main (fixed in 0cb2cb8, Mar 2026, after
  the issue was filed); this PR adds the missing explanation of why the
  capitalized form fails, which is the actual reporter confusion.
• registry-install vs install documented (what each does, when to use
  which), verified against comfy_cli/command/custom_nodes/command.py.
• --fast-deps documented, including which node commands accept it and the
  current reason registry-install does not, verified against the command
  signatures in source.
• Follow-up bug: not needed. The ComfyUI-Impact-Pack failure is a
  case-sensitivity / stale-doc issue (node IDs are the lowercase registry IDs),
  not an install-resolution bug — the working form already ships on main. No
  resolver change is in scope (per the ticket's out-of-scope note).

Judgment calls / notes

• registry-install is defined with hidden=True in the CLI. I documented it
  anyway (the Registry's install instructions use it and the issue explicitly
  asks for its docs) but left it hidden — unhiding is a behavior change and
  out of scope for a docs ticket.
• The --fast-deps "not accepted by registry-install" claim was verified by
  reading registry_install's signature (it only exposes --force-download),
  and the docs redirect users to comfy node install for that capability
  rather than presenting a dead-end.
• The docs.comfy.org custom-nodes pages that surface these commands live in a
  separate docs repo, not this repo — those are out of scope for this
  comfy-cli README PR and would need a follow-up there if the same guidance is
  wanted on the docs site.

Closes #257

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📥 Commits

Reviewing files that changed from the base of the PR and between 85b62da and 7f679cd.

📒 Files selected for processing (1)

• README.md

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch matt/be-4275-document-registry-install

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch matt/be-4275-document-registry-install

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[github-actions]

🔍 Cursor Review — Consolidated panel

Triggered by @mattmillerai.

✅ No high-signal findings.

Panel: 6/8 reviewers contributed findings.

Reviewers that did not contribute: kimi-k2.5:adversarial (empty), kimi-k2.5:edge-case (empty)