docs: user/getting_started: fix monospace markup

Unlike Markdown, RST uses double backticks for monospace text; single
backticks result in italic text. Use monospace for commands like the
surrounding paragraphs.

docs/user/getting_started.rst

@@ -239,7 +239,7 @@ GLUON_RELEASE
 
 GLUON_SITE_VERSION
   Version of the site configuration. This string is displayed in the config mode
-  and `gluon-info`. If unset, Gluon generates a version string using `git describe`
+  and ``gluon-info``. If unset, Gluon generates a version string using ``git describe``
   on the site folder.
 
 GLUON_TARGET