[VL] GenericBenchmark docs need update when access HDFS file

[Yohahaha]

Description

Seems we need set several environment variables to access HDFS file in GenericBenchmark,

/root/oap-velox/velox/external/hdfs/ArrowHdfsInternal.cpp:366: /opt/HADOOP_COMMON/lib/native/libhdfs.so
Environment variable CLASSPATH not set!
getJNIEnv: getGlobalJNIEnv failed
E20241111 10:31:28.080675 33605 Exceptions.h:66] Line: /root/oap-velox/velox/exec/Driver.cpp:598, Function:operator(), Expression:  Operator::getOutput failed for [operator: TableScan, plan node ID: 0]: string pointer is null, Source: RUNTIME, ErrorCode: INVALID_STATE
I20241111 10:31:28.080758 33605 Task.cpp:1972] Terminating task Gluten_Stage_0_TID_0_VTID_0 with state Failed after running for 2ms
I20241111 10:31:28.080828 33605 Task.cpp:1207] All drivers (1) finished for task Gluten_Stage_0_TID_0_VTID_0 after running for 2ms
terminate called after throwing an instance of 'facebook::velox::VeloxRuntimeError'
  what():  Exception: VeloxRuntimeError
Error Source: RUNTIME
Error Code: INVALID_STATE
Reason: Operator::getOutput failed for [operator: TableScan, plan node ID: 0]: string pointer is null
Retriable: False
Function: operator()

@JkSelf @marin-ma would you help clarify the usage and update docs? thank you!

[JkSelf]

@Yohahaha Yes. We need set this command
export CLASSPATH=$HADOOP_HOME/bin/hdfs classpath --glob
before running generic_benchmark. I will update the docs later. Thanks.

[FelixYBW]

@JkSelf how can we use libhdfs3.so in generic benchmark?