Add blog authoring guide to README

Document author setup, social sharing frontmatter, and recommended
image dimensions (1200x630px) for Open Graph/Twitter cards.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: bamnet

README.md

@@ -21,6 +21,42 @@ Once inside the container (or if you have Ruby and Bundler installed locally):
    bundle exec jekyll serve
    ```
 
+## Writing Blog Posts
+
+### Author setup
+
+Authors are defined in `_data/authors.yml`. Each entry maps a short key to a display name and optional Twitter/X handle:
+
+```yaml
+bamnet:
+  name: Brian Michalski
+  twitter: bamnet
+```
+
+To add yourself, add a new entry to the file with your preferred key and full name. Set `twitter: 0` if you don't have a Twitter/X handle (this prevents the jekyll-seo-tag plugin from generating a bogus `twitter:creator` meta tag).
+
+Use your key in post frontmatter:
+
+```yaml
+author: bamnet
+```
+
+### Social sharing
+
+Every blog post automatically gets Open Graph and Twitter Card meta tags for rich link previews, powered by the `jekyll-seo-tag` plugin. The defaults are:
+
+- **Image:** `/assets/images/blog_banner_1b.jpg` (the blog banner)
+- **Title/Description:** pulled from the post's `title` and first paragraph
+
+To customize a post's social preview, add optional frontmatter:
+
+```yaml
+description: "A short summary for link previews and search results."
+image: /assets/images/my-custom-image.jpg
+```
+
+Custom images should be **1200x630px** (1.91:1 ratio). This is the recommended size for both Open Graph (Facebook, LinkedIn, Slack) and Twitter/X large image cards. Smaller images will work but may appear cropped or blurry on high-DPI screens.
+
 ## Deploying
 
 Deployments are handled via GitHub Actions. Commits to the `master` branch trigger the `.github/workflows/deploy.yml` workflow, which builds the site and deploys it to GitHub Pages.