docs: Add documentation about signing in to Zed (#29054)

Release Notes:

- N/A

docs/src/SUMMARY.md

@@ -4,6 +4,7 @@
 
 - [Getting Started](./getting-started.md)
 - [System Requirements](./system-requirements.md)
+- [Accounts](./accounts.md)
 - [Linux](./linux.md)
 - [Windows](./windows.md)
 - [Telemetry](./telemetry.md)

docs/src/accounts.md

@@ -0,0 +1,26 @@
+# Accounts
+
+Signing in to Zed is not a requirement. You can use most features you'd expect in a code editor without ever doing so. We'll outline the few features that do require signing in, and how to do so, here.
+
+## What Features Require Signing In?
+
+1. All real-time [collaboration features](./collaboration.md).
+2. [LLM-powered features](./assistant/assistant.md), if you are using Zed as the provider of your LLM models. Alternatively, you can [bring and configure your own API keys](./assistant/configuration.md) if you'd prefer, and avoid having to sign in.
+
+## Signing In
+
+Zed uses GitHub's OAuth flow to authenticate users, requiring only the `read:user` GitHub scope, which grants read-only access to your GitHub profile information.
+
+1. Open Zed and click the `Sign In` button in the top-right corner of the window, or run the `client: sign in` command from the command palette (`cmd-shift-p` on macOS or `ctrl-shift-p` on Windows/Linux).
+2. Your default web browser will open to the Zed sign-in page.
+3. Authenticate with your GitHub account when prompted.
+4. After successful authentication, your browser will display a confirmation, and you'll be automatically signed in to Zed.
+
+**Note**: If you're behind a corporate firewall, ensure that connections to `zed.dev` and `collab.zed.dev` are allowed.
+
+## Signing Out
+
+To sign out of Zed, you can use either of these methods:
+
+- Click on the profile icon in the upper right corner and select `Sign Out` from the dropdown menu.
+- Open the command palette and run the `client: sign out` command.