workbench/README.md exceeds Docker Hub's 25,000-byte limit #164

workbench/README.md is 25,069 bytes, 69 bytes over Docker Hub's
25,000-byte limit for repository full descriptions. Every production
build's README push fails as a result:

https://github.com/posit-dev/images-workbench/actions/runs/29355616351/job/87197718403

400 Client Error: Bad Request for url:
https://hub.docker.com/v2/namespaces/posit/repositories/workbench

Introduced in 2ae80a2 ("docs: document PWB_SSSD and sssd disable
options for workbench"), which pushed the file from 24,719 to 25,069
bytes.

Fix: trim the README by 69+ bytes.