Merge #16039: docs: add release note for 14954

0830d40456 docs: add release note for 14954 (fanquake)

Pull request description:

  Adds a release note for #14954: build: Require python 3.5.

ACKs for commit 0830d4:

Tree-SHA512: f647c065ef290fb2acb8f55390d8a8cb197372219700bd48777850646c2410b080e1878582ca08c59e6da37ea1dc2d51724e826894dbb7d8a2b218a3b5464a77

doc/release-notes-14954.md

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+Build system changes
+--------------------
+Python >=3.5 is now required by all aspects of the project. This includes the build systems, test framework and linters. The previously supported minimum (3.4), was EOL in March 2019. See #14954 for more details.