Add community addon to add the ability to customize styles in the story preview area

[Sambego]

Added

• A community addon to add the ability to customize styles in the story preview area.

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[codecov]

Codecov Report

Merging #2007 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2007   +/-   ##
=======================================
  Coverage   21.34%   21.34%           
=======================================
  Files         262      262           
  Lines        5767     5767           
  Branches      699      695    -4     
=======================================
  Hits         1231     1231           
- Misses       4006     4011    +5     
+ Partials      530      525    -5

Impacted Files	Coverage Δ
addons/events/src/components/Event.js	0% <0%> (ø)	⬆️
app/react-native/src/bin/storybook-build.js	0% <0%> (ø)	⬆️
lib/codemod/src/transforms/update-addon-info.js	51.16% <0%> (ø)	⬆️
...ponents/left_panel/stories_tree/tree_decorators.js	33.33% <0%> (ø)	⬆️
lib/components/src/navigation/menu_link.js	0% <0%> (ø)	⬆️
...codemod/src/transforms/update-organisation-name.js	40.62% <0%> (ø)	⬆️
app/react/src/client/preview/error_display.js	0% <0%> (ø)	⬆️
lib/ui/src/modules/ui/configs/handle_keyevents.js	33.33% <0%> (ø)	⬆️
addons/knobs/src/components/types/Boolean.js	11.62% <0%> (ø)	⬆️
addons/storyshots/src/storybook-channel-mock.js	0% <0%> (ø)	⬆️
... and 15 more

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[danielduan]

I think adding general styling sounds really vague.

Perhaps something like Add ability to customize styles in the story preview area?

Also, your readme should include a bit more detail about what the plugin does, a short summary of how it accomplishes it, what the config parameters are (looks like they're just the standard js styles but might be worth a mention), and maybe a screenshot for what it does too.

These are just suggestions from me personally. I don't think we have strict guidelines as to what addons we include in the communities list

[Sambego]

@danielduan thanks for the pointers! I've updated the readme with a screenshot and some information about the accepted parameters.

[danielduan]

looks good, thanks!