Adds information on escaping focus traps in Readme

[redfieldstefan]

Addresses issue #179 : existing focus trap handling is built into react-simple-code-editor, this PR surfaces that information in the README and provides further suggestions if a user would like to implement a more custom solution

[redfieldstefan]

@kitten and @sofiapoh let me know if you would like me to put this somewhere else or re-word or do anything different at all.