help: Update "Create a stream".

- Updates Desktop/Web instructions to follow current help center
  documentation patterns.
- Moves instructions to a Markdown include-block.

help/create-a-stream.md

@@ -9,20 +9,7 @@ If you are an administrator setting up streams for the first time, check out our
 
 ## Create a stream
 
-{start_tabs}
+{!create-a-stream-instructions.md!}
-
-{relative|stream|all}
-
-1. Click **Create stream** on the right.
-
-1. Fill out the requested info, and click **Create**.
-
-!!! warn ""
-
-    **Note**: You will only see the **Create stream** button if you have
-    permission to create streams.
-
-{end_tabs}
 
 ## Stream options
 

help/create-streams.md

@@ -4,20 +4,7 @@
 
 ## How to create a stream
 
-{start_tabs}
+{!create-a-stream-instructions.md!}
-
-{relative|stream|all}
-
-1. Click **Create stream** on the right.
-
-1. Fill out the requested info, and click **Create**.
-
-!!! warn ""
-
-    **Note**: You will only see the **Create stream** button if you have
-    permission to create streams.
-
-{end_tabs}
 
 For more details about stream settings, see [Create a stream](/help/create-a-stream#stream-options).
 

help/include/create-a-stream-instructions.md

@@ -0,0 +1,18 @@
+{start_tabs}
+
+{tab|desktop-web}
+
+{relative|stream|all}
+
+1. Click **Create stream** on the right, or click the **plus**
+   (<i class="fa fa-plus"></i>) icon in the upper right.
+
+1. Fill out the requested info, and click **Create** in the bottom right corner
+   of the form.
+
+!!! warn ""
+
+    **Note**: You will only see the **Create stream** button if you have
+    permission to create streams.
+
+{end_tabs}