Added the content to readme file

I've added all the necessary details in the readme file of this project so that anyone can understand how to use this project.

Author: Chandra0505

projects/Convert_JSON_to_CSV/README.md

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+# Convert a json file into a csv
+This script take a json file as input and generate a csv file in output.
+
+### Prerequisites modules
+* json
+* Run `pip install json` to install required external modules.
+
+### How to run the script
+- Execute `python3 converter.py`