docs: pull the diff update guide out of the README

[floyd-soomgo]

Why

The README carried the whole story of publishing a patch update across two sections: the build hook for each platform, how to archive what it exports, how to release against it, and what asset diffs need on top. That is deployment reference material, and it pushed the install guide out of the way.

What

• docs/diff-updates.md (new) — the guide, in the order a reader meets it: the two kinds of difference a release can offer, exporting the embedded bundle (Android Gradle script, iOS build phase, archiving per binary version, releasing with --binary-bundle-path), then asset diff archives (the order a client tries archives in, and the three conditions that publish diffs).
• docs/diff-updates.ko.md (new) — the same guide in Korean. The two link to each other from the top and match section for section: 7 headings, 5 code blocks, and the same table.
• README.md — 640 → 526 lines. Section 4-2 is gone (asset diffs have nothing to do with the wrapper section 4 sets up) and section 6 becomes 6. Diff Updates (Optional), a single pointer to the guide. The advantages list at the top gains a Diff Updates entry, which it never had, linking to the same guide.
• Inbound links follow the content — cli/README.md, cli/README.ko.md and both telemetry callback documents now point at the guide. The Korean documents point at the Korean guide.

Notes

• Docs only. No source or test changes.
• The last commit also fixes a few sentences, in both languages, that leaned on a demonstrative whose antecedent sat dozens of lines away or in a different table row — the record for a binary-patch-base.json named 56 lines earlier, that download for the table row above it.
• Section 6 states that an asset diff only ships on a release that carries a binary patch, which matches the gate in cli/commands/releaseCommand/release.ts (binaryPatch && bundleDownloader && diffBaseCount > 0).
• All 50 local markdown links across the seven touched files were checked against their targets, anchors included.
• The two language versions are kept in step by hand, so a wording change in one needs the same change in the other.

[floyd-soomgo]

The new docs still need some work to make them easier to understand. Since it looks like this will take some time, I’ll merge this PR for now and work on improving them over the weekend.