Move Jo Cook to retired PSC status

Jo has requested to step back from the PSC: https://thegooddocsproject.groups.io/g/main/message/525?p=,,,20,0,0,0::relevance,,Stepping+back+from+PSC,20,2,0,77773220
Thanks Jo for helping to found this project, and for all the wise advice and contributions you have provided.

Author: camerons

who-are-we.md

@@ -8,7 +8,6 @@ Here we list the people behind this project, as defined by the project's [roles]
 
 * Cameron Shorter, chair
 * Felicity Brand
-* Jo Cook
 * Jared Morgan
 * Erin McKean
 * Clarence Cromwell
@@ -17,6 +16,7 @@ Here we list the people behind this project, as defined by the project's [roles]
 
 Our thanks to previous PSC members:
 
+* Jo Cook
 * Jennifer Rondeau
 * Becky Todd