docs: Fix capitalization of PyCharm

[leeyspaul]

A simple capitalization fix from Pycharm to PyCharm. Found in the docs as recommended in the contributors quickstart guide.

First contribution to Airflow. :)

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[boring-cyborg]

Congratulations on your first Pull Request and welcome to the Apache Airflow community! If you have any issues or are unsure about any anything please check our Contributors' Guide
Here are some useful points:

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