Add `pandas` into `requirements.txt`

[seongsujeong]

Checked for duplicates

Yes - I've already checked

Describe the bug

s1_geocode_stack.py from PR #53 (merged as of Oct 2022) imports pandas This is a reminder that we need to add this module in requirements.txt

What did you expect?

We need to add pandas into requirements.txt in order to use s1_geocode_stack.py

Reproducible steps

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Environment

- Version of this software [e.g. vX.Y.Z]
- Operating System: [e.g. MacOSX with Docker Desktop vX.Y]
...

[vbrancat]

Addresed by #88