docs: fix typos and a broken image URL in top-level READMEs

[andromia3]

WHY are these changes introduced?

Four small, verifiable issues in the two top-of-repo README files.

WHAT is this pull request doing?

`README.md`:
```diff
-Install the latest version of Node.js and [npm]...
+Install the latest version of Node.js and [npm]...
```
Double space before the `[Node.js]` link.

```diff
-You can also use do it through Homebrew on macOS: `brew tap shopify/shopify && brew install shopify-cli`
+You can also do it through Homebrew on macOS: `brew tap shopify/shopify && brew install shopify-cli`
```
Stray `use` in "You can also use do it".

```diff
-## Developing Hydrogen custom storefronts with Shopify CLI ##
+## Developing Hydrogen custom storefronts with Shopify CLI
```
Trailing `##` on the heading (closing markers like that aren't rendered but they show up in auto-generated TOCs and some linters flag them).

`docs/README.md`:
```diff
-<img src="https://github.com/Shopify/shopify-cli/raw/main/assets/logo.png\" alt="Shopify logo" width="150">
+<img src="https://github.com/Shopify/cli/raw/main/assets/logo.png\" alt="Shopify logo" width="150">
```
The `` src pointed at `Shopify/shopify-cli`, which is now archived. The current repo is `Shopify/cli`, and `assets/logo.png` exists there.

How to test your changes?

Docs-only. The README renders differently in each case:

• Hover the "Node.js" link in the rendered "Before you begin" section — the double space is visible.
• Read the "Developing themes" section out loud — "use do it" is visibly wrong.
• The Hydrogen heading's TOC anchor was previously `shopify-cli-` (trailing dash from the `##`).
• `docs/README.md` now pulls the logo from a live repo instead of an archived one.

Post-release steps

None — docs-only.

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes — this is the docs change
• I've considered analytics changes to measure impact — N/A, docs-only
• The change is user-facing, so I've added a changelog entry with `pnpm changeset add` — no changeset needed for docs-only changes