Added microcontroller topic

[oceanthunder]

Please confirm this pull request meets the following requirements:

• I followed the contributing guidelines: https://github.com/github/explore/blob/main/CONTRIBUTING.md.
• I am not the sole author or employee of a company who created either the topic I am modifying/adding or the collection entry I am modifying/adding.

Which change are you proposing?

• Suggesting edits to an existing topic or collection
• Curating a new topic or collection
• Something that does not neatly fit into the binary options above

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Curating a new topic or collection

• I've formatted my changes as a new folder directory, named for the topic or collection as it appears in the URL on GitHub (e.g. https://github.com/topics/[NAME] or https://github.com/collections/[NAME])
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Since microcontrollers are widely used and I thought it needed that curated topic treatment.

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[shaedrich]

Do you mind me asking, what the U in "mcu" stands for?

[adammakesthingsdev]

The U stands for unit :)
Weird acronym but that's the way it is sometimes

[oceanthunder]

yup, saw it in the wikipedia page

[shaedrich]

Ah, thanks for the explanation 👍🏻 So, not the Marvel cinematic universe then 😂

[oceanthunder]

Commited the said changes.

[shaedrich]

LGTM