Script execution environment documentation.

Author: fboender

doc/MANUAL.md

@@ -51,6 +51,7 @@ This is the manual for version %%VERSION%%.
 1. [Script execution](#script_execution)
     - [Validation](#script_validation)
     - [Field Values](#script_fieldvalues)
+    - [Environment](#script_env)
     - [Execution security policy](#script_runas)
 1. [Users](#users)
     - [Passwords](#users_passwords)