add: eyecach to README

Author: hazi

README.md

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 # SpeedLimiter
 
+<img src="README_image.jpg" width="400px" />
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 This is a Gem for execution limits in multi-process and multi-threaded environments. By using Redis, you can limit execution across multiple processes and threads.
 
 It was mainly created to avoid hitting access limits to the API server.