Merge commit '9b0050e9aabe4be65c78ccf292a348f309d50ccd' as 'docs'

```
git subtree add --prefix=docs/ https://github.com/gohugoio/hugoDocs.git master --squash
```

Closes #11925

docs/config/_default/markup.toml

@@ -0,0 +1,40 @@
+defaultMarkdownHandler = "goldmark"
+
+[goldmark.extensions]
+definitionList = true
+footnote = true
+linkify = true
+strikethrough = true
+table = true
+taskList = true
+typographer = true
+
+  [goldmark.extensions.passthrough]
+  enable = true
+
+    [goldmark.extensions.passthrough.delimiters]
+      block = [['\[', '\]'], ['$$', '$$']]
+      inline = [['\(', '\)']]
+
+[goldmark.parser]
+autoHeadingID = true
+autoHeadingIDType = "github"
+
+  [goldmark.parser.attribute]
+  block = true
+  title = true
+
+[goldmark.renderer]
+hardWraps = false
+unsafe = false
+xhtml = false
+
+[highlight]
+style = "trac"
+lineNumbersInTable = true
+noClasses = false
+
+[tableOfContents]
+endLevel = 2
+ordered = false
+startLevel = 2