docs(cli): Explain SLF4J API usage in addition to Log4j API usage

Signed-off-by: Sebastian Schuberth <sebastian@doubleopen.org>

cli/src/main/kotlin/OrtMain.kt

@@ -137,6 +137,11 @@ class OrtMain : CliktCommand(
     }
 
     override fun run() {
+        // This is somewhat dirty: For logging, ORT uses the Log4j API (because of its nice Kotlin API), but Logback as
+        // the implementation (for its robustness). The former API does not provide a way to set the root log level,
+        // only the Log4j implementation does (via org.apache.logging.log4j.core.config.Configurator). However, the
+        // SLF4J API does provide a way to get the root logger and set its level. That is why ORT's CLI additionally
+        // depends on the SLF4J API, just to be able to set the root log level below.
         val rootLogger = LoggerFactory.getLogger(Logger.ROOT_LOGGER_NAME) as Logger
         rootLogger.level = logLevel
 

helper-cli/src/main/kotlin/HelperMain.kt

@@ -108,6 +108,11 @@ internal class HelperMain : CliktCommand(
     }
 
     override fun run() {
+        // This is somewhat dirty: For logging, ORT uses the Log4j API (because of its nice Kotlin API), but Logback as
+        // the implementation (for its robustness). The former API does not provide a way to set the root log level,
+        // only the Log4j implementation does (via org.apache.logging.log4j.core.config.Configurator). However, the
+        // SLF4J API does provide a way to get the root logger and set its level. That is why ORT's CLI additionally
+        // depends on the SLF4J API, just to be able to set the root log level below.
         val rootLogger = LoggerFactory.getLogger(Logger.ROOT_LOGGER_NAME) as Logger
         rootLogger.level = logLevel