Restructure collaboration docs (#43464)

Overview
    - Channels
    - Private calls

---

Up next would be to 

- [ ] Update any zed.dev links to point to items in this structure
- [ ] Update content in these docs (would prefer to do that in a
separate PR from this one)

Release Notes:

- N/A

docs/src/SUMMARY.md

@@ -34,8 +34,9 @@
 - [Command-line Interface](./command-line-interface.md)
 - [Outline Panel](./outline-panel.md)
 - [Code Completions](./completions.md)
-- [Channels](./channels.md)
-- [Collaboration](./collaboration.md)
+- [Collaboration](./collaboration/overview.md)
+  - [Channels](./collaboration/channels.md)
+  - [Private Calls](./collaboration/private-calls.md)
 - [Git](./git.md)
 - [Debugger](./debugger.md)
 - [Diagnostics](./diagnostics.md)

docs/src/authentication.md

@@ -4,7 +4,7 @@ Signing in to Zed is not required. You can use most features you'd expect in a c
 
 ## What Features Require Signing In?
 
-1. All real-time [collaboration features](./collaboration.md).
+1. All real-time [collaboration features](./collaboration/overview.md).
 2. [LLM-powered features](./ai/overview.md), if you are using Zed as the provider of your LLM models. To use AI without signing in, you can [bring and configure your own API keys](./ai/llm-providers.md#use-your-own-keys).
 
 ## Signing In

docs/src/collaboration/channels.md

@@ -1,7 +1,5 @@
 # Channels
 
-At Zed we believe that great things are built by great people working together. We have designed Zed to help every individual work faster and to help teams of people work together more effectively.
-
 ## Overview
 
 Channels provide a way to streamline collaborating for software engineers in many ways, but particularly:
@@ -27,7 +25,7 @@ After joining a channel, you can `Share` a project with the other people there.
 
 When you are editing someone else’s project, you still have the full power of the editor at your fingertips, you can jump to definitions, use the AI assistant, and see any diagnostic errors. This is extremely powerful for pairing, as one of you can be implementing the current method while the other is reading and researching the correct solution to the next problem. And, because you have your own config running, it feels like you’re using your own machine.
 
-See [our collaboration documentation](./collaboration.md) for more details about how this works.
+See [our collaboration documentation](./private-calls.md) for more details about how this works.
 
 ## Notes
 

docs/src/collaboration/overview.md

@@ -0,0 +1,17 @@
+# Collaboration
+
+At Zed, we believe that great things are built by great people working together.
+We have designed Zed to help individuals work faster and help teams of people work together more effectively.
+Zed has two mechanisms for collaborating:
+
+1. [Channels](./channels.md): Ongoing project rooms where team members can share projects, collaborate on code, and maintain ambient awareness of what everyone is working on.
+1. [Private Calls](./private-calls.md): Ad-hoc private collaboration with those in your contacts list.
+
+You will need to [sign in](../authentication.md#signing-in) in order to begin using Zed's collaboration features.
+
+---
+
+> Note: Only collaborate with people that you trust.
+> Since sharing a project gives them access to your local file system, you should not share projects with people you do not trust; they could potentially do some nasty things.
+>
+> In the future, we will do more to prevent this type of access beyond the shared project and add more control over what collaborators can do, but for now, only collaborate with people you trust.

docs/src/collaboration/private-calls.md

@@ -1,8 +1,4 @@
-# Collaboration
-
-Only collaborate with people that you trust. Since sharing a project gives them access to your local file system, you should not share projects with people you do not trust; they could potentially do some nasty things.
-
-In the future, we will do more to prevent this type of access beyond the shared project and add more control over what collaborators can do, but for now, only collaborate with people you trust.
+# Private Calls
 
 ## Adding a collaborator to a call
 
@@ -28,7 +24,7 @@ If someone you want to collaborate with has not yet signed up for Zed, they will
 
 ### Voice chat
 
-When joining a call, Zed will automatically share your microphone with other users in the call, if your OS allows it. This isn't tied to your project. You can disable this for your client via the [`mute_on_join`](./configuring-zed.md#calls) setting.
+When joining a call, Zed will automatically share your microphone with other users in the call, if your OS allows it. This isn't tied to your project. You can disable this for your client via the [`mute_on_join`](../configuring-zed.md#calls) setting.
 
 ## Collaborating on a project
 

docs/src/toolchains.md

@@ -8,7 +8,7 @@ With toolchain selector, you don't need to spend time configuring your language
 You can even select different toolchains for different subprojects within your Zed project. A definition of a subproject is language-specific.
 In collaborative scenarios, only the project owner can see and modify an active toolchain.
 
-In [remote projects](./remote-development.md), you can use the toolchain selector to control the active toolchain on the SSH host. When [sharing your project](./collaboration.md), the toolchain selector is not available to guests.
+In [remote projects](./remote-development.md), you can use the toolchain selector to control the active toolchain on the SSH host. When [sharing your project](./collaboration/overview.md), the toolchain selector is not available to guests.
 
 ## Why do we need toolchains?