Examples / Usage docs for memory_tier

A usage / example doc to be created in a new `/docs/usage` folder, the doc would have an example script or a snippet with an example input and output to showcase the usage of the task.

Start by locating the memory_tier task implementation and reviewing any existing task documentation or examples. Create the /docs/usage folder with an example script or snippet showing representative input and output for memory_tier; done means a newcomer can understand how to use the task from the documented example.

Written by the indexing model from the issue text.