Adding common.bash documentation

README.md

@@ -9,8 +9,15 @@ To use these scripts on your container image construction project, issue these c
 ```
 ```
 
+### common.bash
+
+The installation process will create a common.bash file.  This file should be the central, canonical authority for management of environment variables.  While a subprocess may override them, the files in common.bash should be treated as authoritative defaults.  Processes (e.g. `docker build`, `bats`, inside `Jenkinsfile`) can read this file and process the results therein.
+
+You should edit this file to change the image name, and add any other helpful environment variables.
+
 ## Use
 
+
 ### Building
 
 #### build.sh