Readme enhancements

[jodeev]

Summary

Updated the README to allow people who land on this project to decipher quickly exactly what this project does and doesn't do.

Updated the problem to be more specific. Add the key differentiators of the project. Add target audience and the Why this project is here.

Changes

REAMDE updates:

• updated subtitle
• corrected problem
• Dropped the "shared intent, shared memory shared context", replaced with Alignment, alignment memory, and peer collab environment, added callout about whats delivered now and where project may go, added note about definition of "Session" for mycelium
• New section on alternatives
• New section on who its for and why we're building it
• NOTE: Quick start, Architecture, Development and Built on are unchanged from the original README

[jodeev]

suggestions to replace plurals with neutral language

[jodeev]

Additional suggested fixes

[jodeev]

LGTM