Add support for boilerplate text. (#3005)

.spelling

@@ -539,6 +539,7 @@ webhook
 Keycloak
 OpenID
 Istioctl
+Boilerplates
 
  - search.md
 searchresults

boilerplates/en/example.md

@@ -0,0 +1,2 @@
+This is some boilerplate *markdown* _text_.
+

content/about/contribute/writing-a-new-topic/index.md

@@ -65,6 +65,11 @@ is the best fit for your content:
   </tr>
 </table>
 
+### About blog posts
+
+The Istio blog is intended to contain authoritative posts regarding Istio and technologies or products related to
+Istio. We generally do not publish user or enthusiast posts about using Istio.
+
 ## Naming a topic
 
 Choose a title for your topic that has the keywords you want search engines to find.
@@ -433,6 +438,22 @@ will use when the user chooses to download the file. For example:
 If you don't specify the `downloadas` attribute, then the download name is taken from the `url`
 attribute instead.
 
+## Embedding boilerplate text
+
+You can embed common boilerplate text into any markdown output using the `boilerplate` sequence:
+
+{{< text markdown >}}
+{{</* boilerplate example */>}}
+{{< /text >}}
+
+which results in:
+
+{{< boilerplate example >}}
+
+You supply the name of a boilerplate file to insert at the current location. Boilerplates are
+located in language-specific subdirectories of the `boilerplates` directory. Boilerplates are just
+normal markdown files.
+
 ## Using tabs
 
 If you have some content to display in a variety of formats, it is convenient to use a tab set and display each

layouts/shortcodes/boilerplate.html

@@ -0,0 +1,4 @@
+{{- /* Inserts a boilerplate markdown file into the document. See https://preliminary.istio.io/about/contribute/writing-a-new-topic/#embedding-boilerplate-text for details */ -}}
+{{- $path := printf "boilerplates/%s/%s.md" .Site.Language.Lang (.Get 0) -}}
+{{- $markdown := readFile $path -}}
+{{- markdownify $markdown }}