Chore: Update requirements.txt
When only using/installing the speech data explorer, pandas is not installed but needed to execute the tool. To stream line the process I edited the requirements.txt

# What does this PR do ?

It should help to streamline the process of installing the requirements, since pandas is used but not installed with the original file.

**Collection**: [Note which collection this PR will affect]

# Changelog 
- Added: "pandas" to line 11

# Usage
* When only using the Speech data explorer, in a new python enviroment.

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