[DOC] Instructions for one of the examples in the tutorial needs to be updated

[MMelQin]

Report incorrect documentation

Location of incorrect documentation

Subsection Executing from Shell in Section Creating a Simple Image Processing App in Chapter Tutorials of the User Guide

Describe the problems or issues found in the documentation

The example input file location had changed, now in a sub folder, but the app tries to load the input from another folder and the env var to specify input path is not set in the steps.

Steps taken to verify documentation is incorrect

Follow the steps in the document

Suggested fix for documentation

Add the missing steps to set env var