Add "dont use this.send in componentWillUnmount" section to README

[vovacodes]

Just wanted to clarify a confusing moment: "shall I always call side-effects through sending an action?"
React docs say that you should never call setState in componentWillUnmount and this.send eventually calls setState, so I believe we should make it clear that we shouldn't call this.send in componentWillUnmount either.

What do you think?

[codecov]

Codecov Report

Merging #15 into master will not change coverage.
The diff coverage is n/a.

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[philipp-spiess]

Excellent, thank you!

In general, it's safe to directly call side-effects inside any callbacks of the commit phase as well (cDM, cDU). Using send() in those cases will work but it might also trigger a cascading update which might be unexpected.