Section addressing non-serialiazability of a multithreaded redis about keydb

[JohnSully]

KeyDB provides the same guarantees here as Redis does, namely that EXEC transactions are atomic. Single threading is not required in order to have transactions. If you find a bug where we don't uphold this guarantee that would be an extremely high priority item to fix.

Lua scripts and external modules hold a lock and prevent any other code from running concurrently so they also maintain the same guarantees as before. API changes are required in order to gain more concurrency here and if it is a big enough problem we may look at that in the future. I should be clear the goal here is full compatibility first, and multi-threading second.

I'm reticent to add a section to the ReadMe that effectively says "we're not broken" but if its a common source of confusion it may be necessary.

[JohnSully]

#5 is very similar to this issue, and because of that I've added extra phrasing to the Readme:

KeyDB has full compatibility with the Redis protocol, modules, and scripts. This includes full support for transactions, and atomic execution of scripts.

[JohnSully]

Additional architecture information added: 8a5a513

[JohnSully]

Please reopen if you feel this has not been addressed fully.