Improve help pages with documentation

To make documentation rendered under GitLab UI more readable

* Limit width container
* Increase font-size to 110%
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/assets/stylesheets/pages/help.scss

@@ -37,6 +37,7 @@
 
 .documentation {
   padding: 7px;
+  font-size: 110%;
 }
 
 .card.links-card {

app/views/help/show.html.haml

 - page_title @path.split("/").reverse.map(&:humanize)
+- @content_class = "limit-container-width" unless fluid_layout
+
 .documentation.md.prepend-top-default
   = markdown @markdown

changelogs/unreleased/dz-improve-help-layout.yml

+---
+title: Improve UI of documentation under /help
+merge_request: 18331
+author:
+type: changed