Document logging behavior and dontlog feature

Dockerfile

@@ -1,4 +1,4 @@
-FROM harbor.ntppool.org/perlorg/base-os:3.22.2
+FROM harbor.ntppool.org/perlorg/base-os:3.23.3
 ENV BUILD_VERSION 1
 USER root
 WORKDIR /web

README.md

@@ -19,6 +19,22 @@ To get a shell in the container run
 
 And then run `curl -H 'Host: i.perl.org' localhost` there.
 
+## Logging
+
+Access logs are sent to stdout and error logs to stderr, making them
+available to the container runtime's log collection.
+
+The Apache configuration supports a `dontlog` environment variable. When
+set on a request, that request is excluded from the access log. This is
+useful for health check endpoints that would otherwise fill the logs.
+
+To use it, add a `SetEnvIf` directive in your site configuration:
+
+    SetEnvIf Request_URI "^/ok.txt$" dontlog
+
+This allows `/ok.txt` to serve as a health check endpoint without
+generating access log entries.
+
 ## Production image
 
 The "production image" is at harbor.ntppool.org/library/static-web:latest