updating references and commands in Apache Spark setup doc

[marius-tw]

adjustments

add-to-path commands

within this section updated the image ref for PySpark-installation and some references for the PATH here since I wasn't sure whether it could be common practice to leave out the traling " in PATH-add command like

`export PATH="$JAVA_HOME/bin:$SPARK_HOME/bin`

or

`export PATH="$JAVA_HOME/bin:$SPARK_HOME/bin"`

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pySpark shell png reference

https://github.com/data-derp/exercise-vanilla-spark/blob/main/README.md?plain=1#L34

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Spark shell png reference

https://github.com/data-derp/exercise-vanilla-spark/blob/main/README.md?plain=1#L33