image definition docs for OS users

docs/building-images.md

@@ -38,9 +38,24 @@ operatingSystem:
   kernelArgs:
   - arg1
   - arg2
+  users:
+  - username: user1
+    password: 123
+    sshKey: user1Key
+  - username: user2
+    password: 456
+  - username: user3
+    sshKey: user3Key
 ```
 
 * `kernelArgs` - Optional; Provides a list of flags that should be passed to the kernel on boot.
+* `users` - Optional; Defines a list of operating system users to be created. Each entry is made up of
+  the following fields:
+  * `username` - Required; Username of the user to create. To set the password or SSH key for the root user,
+    use the value `root` for this field.
+  * `password` - Optional; Encrypted password to set for the use (for example, using `openssl passwd -6 $PASSWORD`
+    to generate the value for this field).
+  * `sshKey` - Optional; Full public SSH key to configure for the user.
 
 ## Image Configuration Directory