docs: expand README

Add an Available Skills table summarising each skill's purpose, plus contributor notes covering the per-skill directory layout and the rationale for ignoring .claude/.

README.md

@@ -4,4 +4,23 @@ This repository stores commonly used skills for Claude Code internally.
 
 ## Installation
 
-Clone this repository into `~/.claude/skills` with `git clone git@git.onixbyte.com:onixbyte/claude-code-skills ~/.claude/skills`.
+Clone this repository into `~/.claude/skills` with `git clone git@git.onixbyte.com:onixbyte/claude-code-skills ~/.claude/skills`.
+
+## Available Skills
+
+| Skill | Description |
+|---|---|
+| `british-english` | Apply British English spelling and grammar as a global default for files, commits, and documentation when no project-level language override is set. |
+| `commit-message` | Produce conventional-commit messages from the current staged diff, with optional gitmoji support. |
+| `spring-boot` | Conventions for Spring Boot services on Gradle + Java 21 + Spring Boot 3.5: a strict four-layer architecture (Controller → Service → Manager/Client → Mapper/Repository), with an optional Variant layer for multi-implementation strategies. Covers MyBatis + JPA, Spring Validation, global exception handling, TraceId logging, and SpringDoc OpenAPI. |
+
+## Adding a Skill
+
+1. Create a directory named after the skill: `mkdir my-skill/`.
+2. Add a `SKILL.md` inside it, beginning with the required frontmatter (`name`, `description`).
+3. Open a pull request against `main`.
+
+## Repository Hygiene
+
+- Local Claude Code configuration (`.claude/`) is ignored — keep per-machine settings out of version control.
+- Each skill lives in its own top-level directory named exactly as the `name` field in its `SKILL.md`.