overview.rst missing a newline which caused image to not display

[chrispatterson]

Adding an additional newline after the last paragraph in the "Distributed Airflow architecture" section, so that the diagram_distributed_airflow_architecture.png image will be properly interpreted as an image.

(Trivial I know, but noticed while I was reading the documentation and felt like campsite rules were a good impetus to submit a fix)

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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:

• Pay attention to the quality of your code (ruff, mypy and type annotations). Our prek-hooks will help you with that.
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[Vamsi-klu]

Confirmed the root cause. In RST a .. image:: directive must be separated from the preceding paragraph by a blank line; otherwise docutils folds the directive line into the paragraph and emits it as literal text instead of parsing it as an image. The paragraph ending "Helm chart is one of the ways how to deploy Airflow in K8S cluster." had no blank line before the image line, so the distributed-architecture diagram rendered as raw text. The sibling diagram_dag_processor_airflow_architecture.png directive lower in the same file already has its blank line, so this brings the two into line. Straightforward and correct.