docs(banner): add README

Author: zeroedin

elements/pf-v6-banner/README.md

@@ -0,0 +1,51 @@
+# pf-v6-banner
+
+A full-width banner for communicating short, non-dismissible messages.
+
+## Usage
+
+### Default banner
+
+```html
+<pf-v6-banner>Default banner</pf-v6-banner>
+```
+
+### Status banner with screen reader text
+
+```html
+<pf-v6-banner status="danger" screen-reader-text="Danger banner:">
+  An error has occurred. Contact support for help.
+</pf-v6-banner>
+```
+
+### Sticky color banner
+
+```html
+<pf-v6-banner color="blue" sticky>
+  This banner sticks to the top of its container.
+</pf-v6-banner>
+```
+
+## Divergences from React `Banner`
+
+### Changed API
+
+| React prop | Web component | Difference |
+|---|---|---|
+| `isSticky` | `sticky` attribute | Renamed; dropped `is` prefix |
+| `color` + `status` mutual exclusion | Both accepted | React enforces via TypeScript union types (`color` and `status` cannot both be set). The web component accepts both; `status` takes visual precedence via CSS cascade. |
+
+### Added
+
+| Web component API | Notes |
+|---|---|
+| `--pf-v6-c-banner--BackgroundColor` | Override the default background color |
+| `--pf-v6-c-banner--Color` | Override the default text color |
+| `--pf-v6-c-banner--FontSize` | Override the font size |
+| `--pf-v6-c-banner--PaddingBlockStart` | Override the block padding |
+| `--pf-v6-c-banner--PaddingInlineStart` | Override the inline padding |
+| `--pf-v6-c-banner--BorderColor` | Override the border color (high-contrast mode) |
+| `--pf-v6-c-banner--BorderWidth` | Override the border width (high-contrast mode) |
+| `--pf-v6-c-banner--m-sticky--ZIndex` | Override the z-index when sticky |
+| `--pf-v6-c-banner--m-sticky--BoxShadow` | Override the box shadow when sticky |
+| Per-color/status CSS custom properties | Each color (e.g., `--pf-v6-c-banner--m-red--BackgroundColor`) and status variant has overridable background and text color properties |