Update Tomcat, especially to note the removal of the default webapps

tomcat/content.md

@@ -8,21 +8,23 @@ Apache Tomcat (or simply Tomcat) is an open source web server and servlet contai
 
 # How to use this image.
 
+**Note:** as of [docker-library/tomcat#181](https://github.com/docker-library/tomcat/pull/181), the upstream-provided (example) webapps are *not* enabled by default, per [upstream's security recommendations](https://tomcat.apache.org/tomcat-9.0-doc/security-howto.html#Default_web_applications), but are still available under the `webapps.dist` folder within the image to make them easier to re-enable.
+
 Run the default Tomcat server (`CMD ["catalina.sh", "run"]`):
 
 ```console
-$ docker run -it --rm %%IMAGE%%:8.0
+$ docker run -it --rm %%IMAGE%%:9.0
 ```
 
 You can test it by visiting `http://container-ip:8080` in a browser or, if you need access outside the host, on port 8888:
 
 ```console
-$ docker run -it --rm -p 8888:8080 %%IMAGE%%:8.0
+$ docker run -it --rm -p 8888:8080 %%IMAGE%%:9.0
 ```
 
-You can then go to `http://localhost:8888` or `http://host-ip:8888` in a browser.
+You can then go to `http://localhost:8888` or `http://host-ip:8888` in a browser (noting that it will return a 404 since there are no webapps loaded by default).
 
-The default Tomcat environment in the image for versions 7 and 8 is:
+The default Tomcat environment in the image is:
 
 	CATALINA_BASE:   /usr/local/tomcat
 	CATALINA_HOME:   /usr/local/tomcat
@@ -30,12 +32,4 @@ The default Tomcat environment in the image for versions 7 and 8 is:
 	JRE_HOME:        /usr
 	CLASSPATH:       /usr/local/tomcat/bin/bootstrap.jar:/usr/local/tomcat/bin/tomcat-juli.jar
 
-The default Tomcat environment in the image for version 6 is:
-
-	CATALINA_BASE:   /usr/local/tomcat
-	CATALINA_HOME:   /usr/local/tomcat
-	CATALINA_TMPDIR: /usr/local/tomcat/temp
-	JRE_HOME:        /usr
-	CLASSPATH:       /usr/local/tomcat/bin/bootstrap.jar
-
 The configuration files are available in `/usr/local/tomcat/conf/`. By default, no user is included in the "manager-gui" role required to operate the "/manager/html" web application. If you wish to use this app, you must define such a user in `tomcat-users.xml`.