docs: add "Who's using gh-image" section to README

[drogers0]

Adds a Who's using gh-image section between Use with AI agents and Authentication, showcasing three projects that run gh-image in their review and documentation pipelines.

Entries

Project	Usage site	How they use it
NousResearch/hermes-agent ★ 220k+	publish-e2e-evidence.yml	Posts E2E screenshots inline on every PR from CI, unattended, via a dedicated attachment bot account scoped to that repo
openshift/console ★ 450+ (Red Hat)	upload-evidence.sh	Its /qa-verify agent skill uploads full-resolution QA evidence for reviewers
Simpleyyt/ai-manus ★ 1.5k+	demo-videos/SKILL.md	A demo-videos skill publishes the README demo reels

Verification

Every claim was checked against source rather than taken on trust:

• All three repositories confirmed to exist, with star counts read from the API. Badges use 220k+ / 450+ / 1.5k+ so they stay accurate as the repos grow.
• Each usage site was read directly; descriptions reflect what the code and skill files actually do.
• All six outbound links return HTTP 200.
• The hermes-agent bot-account detail comes from that PR's own description: "The attachment bot is a dedicated account limited to this repository."
• The rendered output was verified through GitHub's /markdown API to confirm the layout survives HTML sanitization.

Layout notes

• Two single-row HTML tables, not one two-row table. GitHub's stylesheet shades even-numbered rows (tr:nth-child(2n)), which tinted the second row's background. Inline style is stripped so it cannot be overridden, but one row per table keeps every row at nth-child(1) and unshaded. Both carry width="100%" so the two boxes align (GitHub sizes tables to max-content otherwise).
• HTML, not markdown. Inline style is stripped, so CSS grid is impossible; tables are the only way to get column alignment. border="0" is also stripped, so cell gridlines are unavoidable.
• Cell content is plain HTML (<b>, <code>, <a>) because markdown is not reliably processed inside <td> — backticks and ** would render literally.
• Logos are wrapped in repo links. GitHub otherwise auto-links a bare image to the raw avatar file, so clicking a logo would open the image instead of the project.
• Stars use ★ rather than a literal ★, so the character cannot be mangled by editor encoding.
• Row 1 is a full-width hero card; row 2 holds two balanced cards (descriptions within 3 characters of each other, so they render at the same height).

If a fourth project is added later, drop the colspan="2" on row 1 to make a clean 2×2.