update getting started guide

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Please check if the PR fulfills these requirements

• [x] The PR has no duplicates (please search among the Pull Requests before creating one)
• [x] The PR follows our contributing guidelines
• [x] Tests for the changes have been added (for bug fixes / features)
• [x] Docs have been added / updated (for bug fixes / features)
• [ ] UPGRADING.md has been updated with a migration guide (for breaking changes)

• What kind of change does this PR introduce?

docs update. I follow the getting started guide and the upload step only left a cryptic message (avrdude: jtagmkII_initialize(): Cannot locate "flash" and "boot" memories in description) even though it succeeded. I added the -v so the output is more useful for a first timer

• What is the current behavior?

• What is the new behavior?

• Does this PR introduce a breaking change, and is titled accordingly?

• Other information:

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