README.rst fix

Merged Vladimir Petrigo requested to merge readme-fix into master

During our QA session we have revealed issues that may lead to a build fail. For the repo init command the source brach is left as node-red. After merge it does not exist anymore and it may confuse one who tries to build an image for Vesta.

Also during the test session our QA engineer met an issue with wrong locales, so we would like to propose to add some additional information to the README file to workaround that issue.

And to improve the readability of the README file we refactor code format a little by using reStructuredText extensions.

Reference test session

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