docs: add slack plugin install steps for coding agents (#53)

Author: mwbrooks

README.md

@@ -7,6 +7,46 @@ It's recommended to use a [developer sandbox](https://docs.slack.dev/tools/devel
 1. Join the [Slack Developer Program](https://api.slack.com/developer-program) if you haven't already
 2. [Provision a sandbox workspace](https://docs.slack.dev/tools/developer-sandboxes/#provision)
 
+## Claude Code, Codex, Cursor, and Other Coding Agents
+
+Install the [Slack MCP and Skills Plugin](https://docs.slack.dev/ai/slack-skills-plugin/) so your coding agent can create, run, and deploy Slack apps, look up Web API methods and scopes, and build Block Kit without guessing.
+
+### Claude Code
+
+Run this in a Claude Code session:
+
+```
+/plugin install slack@claude-plugins-official
+```
+
+### Codex
+
+Run this in your terminal:
+
+```sh
+codex plugin marketplace add slackapi/slack-skills-plugin
+codex plugin add slack@slack
+```
+
+### Cursor
+
+Run this in a Cursor Agent chat:
+
+```
+/add-plugin slack
+```
+
+### Other agents
+
+Install the skills with `npx skills`, using your [agent's identifier](https://github.com/vercel-labs/skills#supported-agents):
+
+```sh
+npx skills add slackapi/slack-skills-plugin -y -a <agent>
+
+# For example, OpenCode
+npx skills add slackapi/slack-skills-plugin -y -a opencode
+```
+
 ## Installation
 
 ### Using Slack CLI