Add references to Content guide alongside Style guide (#16101)

Add references to the Content guide where the Style guide was
mentioned.
Update the Contribute page (_index.md)
Make Style and Content linkable everywhere
Changed bullet list to numbered list in Content Guide to make referring
to sections easier.
Reverted change to bullet list - beyond scope of this PR

Signed-off-by: Aimee Ukasick <aimeeu.opensource@gmail.com>

content/en/docs/contribute/style/page-templates.md

@@ -215,7 +215,8 @@ An example of a published topic that uses the tutorial template is
 
 {{% capture whatsnext %}}
 
-- Learn about the [style guide](/docs/contribute/style/style-guide/)
+- Learn about the [Style guide](/docs/contribute/style/style-guide/)
+- Learn about the [Content guide](/docs/contribute/style/content-guide/)
 - Learn about [content organization](/docs/contribute/style/content-organization/)
 
 {{% /capture %}}