Update README.md

Author: alelom

README.md

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 # Python Concurrent (thread-safe) collections
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 ## tl;dr
 
 Despite what many people think, Python's built-in `list`, `dict`, and `deque` are thread-safe for [_some operations_, but not all](https://docs.python.org/3/faq/library.html#what-kinds-of-global-value-mutation-are-thread-safe). This created a lot of confusion in the Python community.