Create session-storage.md user-facing document #347

This document will serve the same purpose as the other docs/ documents like docs/hitl.md and docs/telemetry.md giving the users the information necessary to take advantage of session-storage.

These documents are currently in the process of being moved from this repo to mezmo/documentation under the aura directory

• This is being done via this PR
• Once the "move docs" PR is merged, this session-storage.md doc should be created within mezmo/documentation repo at aura/session-storage.md.