help center: Improve documentation on the ? in-app reference.

Adds a sentence at the end of the intro section of each help center
page explaining that you can pull up a Keyboard shortcuts, Message
formatting, and Search filters reference from inside the app.

Adds/updates the in-app help section at the bottom of the page with
instructions for opening the reference.

Fixes #23758.

templates/zerver/help/format-your-message-using-markdown.md

@@ -3,9 +3,10 @@
 [//]: # (All screenshots here require line-height: 22px and font-size: 16px in .message-content.)
 [//]: # (Requires some additional fiddling for the LaTeX picture, inline code span, and maybe a few others.)
 
-Zulip uses a variant of
-[GitHub Flavored Markdown](https://github.com/adam-p/markdown-here/wiki/Markdown-Cheatsheet)
-to allow you to easily format your messages.
+Zulip uses a variant of Markdown to allow you to easily format your
+messages. There is a convenient [**message formatting
+reference**](#message-formatting-reference) in the Zulip app that you
+can use whenever you need a reminder of the formatting syntax below.
 
 * [Emphasis](#emphasis)
 * [Lists](#lists)
@@ -279,15 +280,16 @@ Under the line
 
 ![Markdown paragraph](/static/images/help/markdown-paragraph.png)
 
-## In-app help
+## Message formatting reference
 
-A summary of the formatting syntax is available in-app.
+A summary of the formatting syntax above is available in the Zulip app.
 
 {start_tabs}
 
 {!start-composing.md!}
 
-1. Click <i class="fa fa-question"></i> at the bottom of the compose box.
+1. Click the **question mark** (<i class="fa fa-question"></i>) icon at the
+   bottom of the compose box.
 
 {end_tabs}
 

templates/zerver/help/keyboard-shortcuts.md

@@ -1,8 +1,9 @@
 # Keyboard shortcuts
 
 Everything in Zulip can be done with the mouse, but mastering a few keyboard
-shortcuts will change your experience of the app. Start with the basics
-below, and add more to your repertoire as needed.
+shortcuts will change your experience of the app. Start with the basics below,
+and use the convenient [**keyboard shortcuts reference**](#keyboard-shortcuts-reference)
+in the Zulip app to add more to your repertoire as needed.
 
 * [The basics](#the-basics)
 * [Navigation](#navigation)
@@ -219,3 +220,19 @@ Keyboard navigation (e.g. arrow keys) works as expected.
 * **View stream messages**: <kbd>Shift</kbd> + <kbd>V</kbd>
 
 * **Toggle subscription**: <kbd>Shift</kbd> + <kbd>S</kbd>
+
+
+## Keyboard shortcuts reference
+
+A summary of the keyboard shortcuts above is available in the Zulip app.
+
+{start_tabs}
+
+1. Click the **keyboard** (<i class="fa fa-keyboard-o"></i>) icon at the bottom
+   of the app, just below the right sidebar.
+
+{end_tabs}
+
+## Related articles
+
+* [Reading strategies](/help/reading-strategies)

templates/zerver/help/search-for-messages.md

@@ -1,7 +1,10 @@
 # Searching for messages
 
-Zulip has a powerful search engine under its hood. You can search for messages using
-keywords and filters via the search bar at the top of the app.
+It's easy to find the right conversation with Zulip's powerful full-text search.
+You can search for messages using keywords and filters via the search bar at the
+top of the app. There is a convenient [**search filters reference**](#search-filters-reference)
+in the Zulip app that you can use whenever you need a reminder of the search
+filters below.
 
 ## Keyword search
 
@@ -143,6 +146,19 @@ When you search Zulip, the URL shown in the address bar of the Zulip web app is
 permanent link to your search. You can share this link with others, and they
 will see *their own* search results for your query.
 
+## Search filters reference
+
+A summary of the search filters above is available in the Zulip app.
+
+{start_tabs}
+
+1. Click the **keyboard** (<i class="fa fa-keyboard-o"></i>) icon at the bottom
+   of the app, just below the right sidebar.
+
+1. Switch to the **Search filters** tab.
+
+{end_tabs}
+
 ## Related articles
 
 * [Configure multi-language search](/help/configure-multi-language-search)