Examples / Usage docs for memory_index

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_index task and reviewing its expected input and output. Create the new docs/usage folder with a usage document containing an example script or snippet, an example input, and the corresponding output; it is done when a reader can understand how to use memory_index from the document alone.

Written by the indexing model from the issue text.