help: Update "Share and upload files" article.

- Adds via-markdown instructions block.
- Adds via-compose-box-buttons instructions block.
- Documents option to select multiple files.
- Adds named image file example section.

help/animated-gifs-from-giphy.md

@@ -67,3 +67,6 @@ recipients of GIFs from GIPHY.
 
 [configure-giphy]: https://zulip.readthedocs.io/en/stable/production/giphy-gif-integration.html
 
+## Related articles
+
+* [Share and upload files](/help/share-and-upload-files)

help/share-and-upload-files.md

@@ -1,21 +1,58 @@
 # Share and upload files
 
-Attach files to messages, including images, documents, sound, and video.
+Zulip supports attaching multiple files to messages, including images,
+documents, sound, and video. You can edit the names of the files others see
+after you upload them.
 
-First, [open the compose box](/help/open-the-compose-box). Then
+Zulip will automatically generate a **thumbnail** for each file when you send
+the message, if it can. Image thumbnails will be shown directly in the message,
+and you can click on a thumbnail to [view the full image](/help/view-and-browse-images).
 
-* **Drag and drop** files into the compose box.
+## Uploading files
-* **Copy and paste** files into the compose box.
-* Click the **paperclip** (<i class="fa fa-paperclip"></i>) icon at
-  the bottom of the compose box to find files on your computer.
 
-Zulip will insert a link to the file, in Markdown format:
+{start_tabs}
-`[link text](URL)`. You can modify the `link text` to whatever you want.
 
-Zulip will automatically generate a **thumbnail** of the file when you send
+{tab|via-markdown}
-it, if it can. You can
+
-[preview the message](/help/preview-your-message-before-sending) before
+{!start-composing.md!}
-sending to see what the thumbnail will look like.
+
+1. Drag and drop files, or copy and paste one or more files into the compose
+   box. Zulip will upload the files, and insert named links using
+   [Markdown formatting](/help/format-your-message-using-markdown#links):
+   `[Link text](URL)`.
+
+1. _(optional)_ Modify the link text as desired.
+
+{tab|via-compose-box-buttons}
+
+{!start-composing.md!}
+
+1. Click the **paperclip** (<i class="fa fa-paperclip"></i>) icon at
+   the bottom of the compose box to select one or more files. Zulip will upload
+   the files, and insert named links using
+   [Markdown formatting](/help/format-your-message-using-markdown#links):
+   `[Link text](URL)`.
+
+1. _(optional)_ Modify the link text as desired.
+
+{end_tabs}
+
+!!! tip ""
+
+    You can [preview the message](/help/preview-your-message-before-sending)
+    before sending to see what your uploaded files will look like.
+
+## Named file example
+
+### What you type
+
+```
+[A whale of a good time](https://your.zulip.domain/user_uploads/1/46/IPvysqXEtiTG1ZdNBrwAZODi/whale-time.png)
+```
+
+### What it looks like
+
+![Markdown image](/static/images/help/markdown-image.png)
 
 ## Troubleshooting info
 
@@ -29,3 +66,4 @@ This limit can be changed by the server administrator.
 
 * [Manage your uploaded files](/help/manage-your-uploaded-files)
 * [View and browse images](/help/view-and-browse-images)
+* [Animated GIFs](/help/animated-gifs-from-giphy)