feat: add slack app install page for app verification (#1260)

as part of the review process with the Slack App marketplace, we are
supposed to have a page somewhere that has installation instructions for
our Slack app. I figured Agent Builder docs was the easiest place to put
that.

---------

Co-authored-by: Kathryn May <44557882+katmayb@users.noreply.github.com>

Author: samecrowder

src/docs.json

@@ -1309,7 +1309,8 @@
             "pages": [
               "langsmith/agent-builder",
               "langsmith/agent-builder-setup",
-              "langsmith/agent-builder-tools"
+              "langsmith/agent-builder-tools",
+              "langsmith/agent-builder-slack-install"
             ]
           },
           {

src/langsmith/agent-builder-slack-install.mdx

@@ -0,0 +1,49 @@
+---
+title: Install LangSmith Agent Builder for Slack
+description: Connect the LangSmith Agent Builder to your Slack workspace to power AI agents.
+sidebarTitle: Slack installation
+mode: wide
+---
+
+After installation, your agents will be able to:
+
+- Send direct messages.
+- Post to channels.
+- Read thread messages.
+- Reply in threads.
+- Read conversation history.
+
+LangSmith Agent Builder integrates your agents with Slack for secure, context-aware communication inside your Slack workspace.
+
+## How to install
+
+To install the LangSmith Agent Builder for Slack:
+
+1. Navigate to Agent Builder in your [LangSmith workspace](https://smith.langchain.com).
+2. Create or edit an agent.
+3. Add Slack as a trigger or enable Slack tools.
+4. When prompted, authorize the Slack connection.
+5. Follow the OAuth flow to grant permissions to your Slack workspace.
+
+The app will be installed automatically when you complete the authorization.
+
+## Permissions
+
+The LangSmith Agent Builder requires the following permissions to your Slack workspace:
+
+- **Send messages** - Send direct messages and post to channels
+- **Read messages** - Read channel history and thread messages
+- **View channels** - Access basic channel information
+- **View users** - Look up user information for messaging
+
+These permissions enable agents to communicate effectively within your Slack workspace.
+
+## Getting started
+
+After installation, configure your agent:
+
+1. Set up Slack as a trigger to activate your agent when messages are received.
+2. Enable Slack tools to allow your agent to send messages.
+3. Configure which channels or users your agent should monitor.
+
+For full setup instructions, see the [Agent Builder documentation](/langsmith/agent-builder).