Create docs/cli directory

This PR creates a directory for CLI-focused design documents to help
keep our design repo a bit more organized.

I also updated the README to clarify that in practice we're using this
as a repo of design artifacts for all of InstructLab and not just
changes that cross multiple repositories. This can always evolve over
time, but it reflects our current reality right now.

Signed-off-by: Russell Bryant <[email protected]>

Author: russellb

README.md

@@ -1,8 +1,8 @@
 # InstructLab Developer Documentation
 
 This repository contains design artifacts that define the architecture and
-design of cross-component interactions in the InstructLab project. The repo
-also serves as a home for technical policies that apply across all components.
+design of components in the InstructLab project. The repo also serves as a home
+for technical policies that apply across all components.
 
 ## Governance