Updated readme

Author: mblaschke

README.md

@@ -167,7 +167,7 @@ Port          | 11211
 
 Environment           | Description
 --------------------- | -------------
-DOCUMENT_ROOT         | Document root for Nginx and Apache HTTPD
+DOCUMENT_ROOT         | Document root for Nginx and Apache HTTPD, can be absolute or relative (to /docker inside the container).
 <br>                  |
 TYPO3_CONTEXT         | Context for TYPO3, can be used for TypoScript conditions and AdditionalConfiguration
 FLOW_CONTEXT          | Context for FLOW and NEOS