Fix: fix missing slash in spark script (#1334)

Author: xleoken

docs/source/user-guide/installation.md

@@ -81,7 +81,7 @@ $SPARK_HOME/bin/spark-shell \
     --conf spark.driver.extraClassPath=$COMET_JAR \
     --conf spark.executor.extraClassPath=$COMET_JAR \
     --conf spark.plugins=org.apache.spark.CometPlugin \
-    --conf spark.shuffle.manager=org.apache.spark.sql.comet.execution.shuffle.CometShuffleManager
+    --conf spark.shuffle.manager=org.apache.spark.sql.comet.execution.shuffle.CometShuffleManager \
     --conf spark.comet.explainFallback.enabled=true \
     --conf spark.memory.offHeap.enabled=true \
     --conf spark.memory.offHeap.size=16g \