web(playground): add Folding Headings section to nomadnet guide

- Added +> / -> and #!fold syntax to the playground seed.
- Updated Table of Contents with the new section.

Author: Ivan

web/static/data/nomadnet_guide.mu

@@ -31,6 +31,7 @@ With micron you can easily create structured documents and pages with formatting
  `F79d`_`[Fields & Requests`#fields-requests]`_`f
  `F79d`_`[Comments`#comments]`_`f
  `F79d`_`[Partials`#partials]`_`f
+ `F79d`_`[Folding Headings`#folding-headings]`_`f
  `F79d`_`[Literals`#literals]`_`f
  `F79d`_`[Closing Remarks`#closing-remarks]`_`f
 
@@ -191,6 +192,25 @@ Wait! It's worth noting that we can also create sections without headings. They
 ``
 
 
+>>Folding Headings
+
+You can make any heading collapsible by prefixing the line with \`+> for an expanded section or \`-> for a collapsed one. Use \`#!fold glyph_open [glyph_closed] to customise the disclosure glyph.
+
+Here is an example:
+
+`Faaa
+`=
++> Open by default
+This content is visible.
+
+-> Collapsed by default
+This content is hidden until expanded.
+
+#!fold v >
+`=
+``
+
+
 >Colors
 
 Foreground colors can be specified with the \`F tag, followed by three hexadecimal characters. To return to the default foreground color, use the \`f tag. Background color is specified in the same way, but by using the \`B and \`b tags.
@@ -551,6 +571,7 @@ With micron you can easily create structured documents and pages with formatting
  `F79d`_`[Fields & Requests`#fields-requests]`_`f
  `F79d`_`[Comments`#comments]`_`f
  `F79d`_`[Partials`#partials]`_`f
+ `F79d`_`[Folding Headings`#folding-headings]`_`f
  `F79d`_`[Literals`#literals]`_`f
  `F79d`_`[Closing Remarks`#closing-remarks]`_`f
 
@@ -711,6 +732,25 @@ Wait! It's worth noting that we can also create sections without headings. They
 ``
 
 
+>>Folding Headings
+
+You can make any heading collapsible by prefixing the line with \`+> for an expanded section or \`-> for a collapsed one. Use \`#!fold glyph_open [glyph_closed] to customise the disclosure glyph.
+
+Here is an example:
+
+`Faaa
+`=
++> Open by default
+This content is visible.
+
+-> Collapsed by default
+This content is hidden until expanded.
+
+#!fold v >
+`=
+``
+
+
 >Colors
 
 Foreground colors can be specified with the \`F tag, followed by three hexadecimal characters. To return to the default foreground color, use the \`f tag. Background color is specified in the same way, but by using the \`B and \`b tags.