Improve documentation for react-native : clarify where left pane is

[lukewlms]

I thought at first the left pane would be somewhere in my app, but this is referring to a left pane in the web browser.

Issue:

What I did

How to test

Is this testable with jest or storyshots?

Does this need a new example in the kitchen sink apps?

Does this need an update to the documentation?

If your answer is yes to any of these, please make sure to include it in your PR.

[codecov]

Codecov Report

Merging #1901 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1901   +/-   ##
=======================================
  Coverage   21.31%   21.31%           
=======================================
  Files         257      257           
  Lines        5737     5737           
  Branches      694      694           
=======================================
  Hits         1223     1223           
- Misses       3968     3988   +20     
+ Partials      546      526   -20

Impacted Files	Coverage Δ
app/vue/src/server/config/babel.js	0% <0%> (-100%)	⬇️
app/vue/src/server/babel_config.js	0% <0%> (-77.42%)	⬇️
app/react-native/src/bin/storybook-start.js	0% <0%> (ø)	⬆️
...res__/update-addon-info/update-addon-info.input.js	0% <0%> (ø)	⬆️
lib/ui/src/modules/ui/libs/hierarchy.js	48.8% <0%> (ø)	⬆️
lib/ui/src/modules/ui/containers/down_panel.js	23.52% <0%> (ø)	⬆️
addons/knobs/src/components/types/Number.js	8.06% <0%> (ø)	⬆️
addons/info/src/components/PropVal.js	41.41% <0%> (ø)	⬆️
addons/knobs/src/components/types/Object.js	5.81% <0%> (ø)	⬆️
addons/info/src/components/markdown/htags.js	30% <0%> (ø)	⬆️
... and 22 more

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[ndelangen]

Can totally understand the confusion, thanks for clearing this up!

If you find any other improvements for our react-native docs, keep the PRs coming 😉 👍 😍