Add a FAQ entry for shared config with next

[tmeasday]

Issue: It's not trivial to reuse config between next and SB, this adds an example

[codecov]

Codecov Report

Merging #1390 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1390   +/-   ##
=======================================
  Coverage   14.35%   14.35%           
=======================================
  Files         201      201           
  Lines        4613     4613           
  Branches      519      497   -22     
=======================================
  Hits          662      662           
- Misses       3501     3532   +31     
+ Partials      450      419   -31

Impacted Files	Coverage Δ
app/react/src/server/babel_config.js	44.82% <0%> (ø)	⬆️
addons/events/src/components/Event.js	0% <0%> (ø)	⬆️
addons/knobs/src/components/WrapStory.js	12% <0%> (ø)	⬆️
addons/info/src/components/markdown/code.js	0% <0%> (ø)	⬆️
addons/info/src/components/Node.js	0% <0%> (ø)	⬆️
lib/ui/src/modules/ui/configs/init_panels.js	25% <0%> (ø)	⬆️
app/react-native/src/preview/story_kind.js	0% <0%> (ø)	⬆️
.../src/manager/containers/CommentsPanel/dataStore.js	34.78% <0%> (ø)	⬆️
addons/storyshots/src/require_context.js	0% <0%> (ø)	⬆️
...rc/modules/ui/components/left_panel/text_filter.js	33.33% <0%> (ø)	⬆️
... and 12 more

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[shilman]

LGTM!