[Docs]: add slack integration docs (#8903)

Co-authored-by: mamoodi <mamoodiha@gmail.com>
Co-authored-by: openhands <openhands@all-hands.dev>

docs/README.md

@@ -0,0 +1,17 @@
+# Setup
+
+```
+npm install -g mint
+```
+
+or 
+
+```
+yarn global add mint
+```
+
+# Preview
+
+```
+mint dev
+```

docs/docs.json

@@ -34,7 +34,8 @@
                 "group": "Integrations",
                 "pages": [
                   "usage/cloud/github-installation",
-                  "usage/cloud/gitlab-installation"
+                  "usage/cloud/gitlab-installation",
+                  "usage/cloud/slack-installation"
                 ]
               },
               "usage/cloud/cloud-ui",

docs/usage/cloud/slack-installation.mdx

@@ -0,0 +1,52 @@
+---
+title: Slack Integration - Coming soon...
+description: This guide walks you through installing the OpenHands Slack app.
+---
+
+<Warning>This integration is not live yet, but will be available soon.</Warning>
+
+## Prerequisites
+
+- You are a slack workspace admin
+- Access to OpenHands Cloud
+
+## Installation Steps
+
+1. Log in to [OpenHands Cloud](https://app.all-hands.dev)
+2. Click the button below to OpenHands Slack App <a target="_blank" href="https://slack.com/oauth/v2/authorize?client_id=7477886716822.8729519890534&scope=app_mentions:read,chat:write,users:read,channels:history,groups:history,mpim:history,im:history&user_scope=channels:history,groups:history,im:history,mpim:history"><img alt="Add to Slack" height="40" width="139" src="https://platform.slack-edge.com/img/add_to_slack.png" srcSet="https://platform.slack-edge.com/img/add_to_slack.png 1x, https://platform.slack-edge.com/img/add_to_slack@2x.png 2x" /></a>
+3. In the top right corner, select the workspace to install the OpenHands Slack app.
+4. Review permissions and click allow
+
+## Working With the Slack App
+
+To start a new conversation, you can mention `@openhands` in a new message or a thread inside any Slack channel.
+
+Once a conversation is started, all thread messages underneath it will be follow-up messages to OpenHands.
+
+To send follow-up messages for the same conversation, mention `@openhands` in a thread reply to the original message. You must be the user who started the conversation.
+
+## Example conversation
+
+### Start a new conversation, and select repo
+
+Conversation is started by mentioning `@openhands`.
+
+![slack-create-convo.png](/static/img/slack-create-convo.png)
+
+### See agent response and send follow up messages
+
+Initial request is followed up by mentioning `@openhands` in a thread reply.
+
+![slack-results-and-follow-up.png](/static/img/slack-results-and-follow-up.png)
+
+## Pro tip
+
+You can mention a repo name when starting a new conversation in the following formats
+
+1. "My-Repo" repo (e.g `@openhands in the openhands repo ...`)
+2. "All-Hands-AI/OpenHands" (e.g `@openhands in All-Hands-AI/OpenHands ...`)
+
+The repo match is case insensitive. If a repo name match is made, it will kick off the conversation.
+If the repo name partially matches against, multiple repos, you'll be asked to select a repo from the filtered list.
+
+![slack-pro-tip.png](/static/img/slack-pro-tip.png)