help: Document bot types in add-a-bot-or-integration.

templates/zerver/help/add-a-bot-or-integration.md

@@ -7,8 +7,9 @@ Bots and integrations are features that are accessible to all members of an orga
 {!go-to-the.md!} [Your bots](/#settings/your-bots)
 {!settings.md!}
 
-2. On this page, under the **Add a new bot** view, you can enter a name, an email, and
-optionally an avatar for your bot. Then click the **Create bot** button to create your bot.
+2. On this page, under the **Add a new bot** view, enter the bot type,
+   a name, an email, and optionally an avatar for your bot.
+   Then click the **Create bot** button to create your bot.
 
     ![Bots page](/static/images/help/add_a_new_bot.png)
 
@@ -22,6 +23,25 @@ configuration file (`.zuliprc`) which you will need for integrations that you wo
 to use with this bot. You can click on the download
 (<i class="icon-vector-download-alt"></i>) icon to download your `.zuliprc` file.
 
+### Bot types
+
+You can create three types of bots:
+
+![Bot types](/static/images/help/bot_types.png)
+
+* **Generic bot:** A generic bot can send *and* receive messages.
+
+* **Incoming webhook:**  The API keys for such bots are limited to
+  only sending messages and can't receive messages. Thus, this bot
+  type lessens the security risks associated with exposing such API
+  keys to third-party services, since they can't be used to read
+  messages.
+
+* **Outgoing webhook:** Bots of this type are the same as a
+  **Generic bot**, except **Outgoing webhooks** bots have an extra field
+  for the base URL of the third-party service being requested.
+  **Outgoing webhook** bots send POST requests to this base URL.
+
 ## Add an integration
 
 The [Integrations page](/integrations) offers a complete list of all the