Fix introduction page header

[lachlanjc]

Issue: Introduction page on docs looks wrong.

I think this fixes it? :)

Current intro page:

[codecov]

Codecov Report

Merging #2757 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2757   +/-   ##
=======================================
  Coverage   35.73%   35.73%           
=======================================
  Files         433      433           
  Lines        9430     9430           
  Branches      983     1006   +23     
=======================================
  Hits         3370     3370           
+ Misses       5422     5362   -60     
- Partials      638      698   +60

Impacted Files	Coverage Δ
app/vue/src/server/config/babel.js	0% <0%> (-100%)	⬇️
app/polymer/src/server/babel_config.js	0% <0%> (-76.67%)	⬇️
app/react/src/server/utils.js	0% <0%> (-53.58%)	⬇️
...dons/actions/src/lib/types/object/getObjectName.js	62.5% <0%> (ø)	⬆️
.../src/modules/ui/components/stories_panel/header.js	29.62% <0%> (ø)	⬆️
...ddons/actions/src/containers/ActionLogger/index.js	49.25% <0%> (ø)	⬆️
addons/info/src/components/types/Shape.js	68.62% <0%> (ø)	⬆️
.../ui/src/modules/ui/components/addon_panel/index.js	34.78% <0%> (ø)	⬆️
addons/actions/src/lib/decycle.js	53.52% <0%> (ø)	⬆️
addons/actions/src/lib/util/prepareArguments.js	57.14% <0%> (ø)	⬆️
... and 59 more

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