Add READMEs for each puzzle

Author: gahjelle

advent-of-code/solutions/2019/01_the_tyranny_of_the_rocket_equation/README.md

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+# Day 1, 2019: The Tyranny of the Rocket Equation
+
+Resources:
+
+- **Puzzle:** [adventofcode.com](https://adventofcode.com/2019/day/1)
+- **Solution:** [realpython.com](https://realpython.com/python-advent-of-code/#practicing-advent-of-code-day-1-2019)

advent-of-code/solutions/2020/01_report_repair/README.md

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+# Day 1, 2020: Report Repair
+
+Resources:
+
+- **Puzzle:** [adventofcode.com](https://adventofcode.com/2020/day/1)
+- **Solution:** [realpython.com](https://realpython.com/python-advent-of-code/#the-structure-of-a-solution)

advent-of-code/solutions/2020/05_binary_boarding/README.md

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+# Day 5, 2020: Binary Boarding
+
+Resources:
+
+- **Puzzle:** [adventofcode.com](https://adventofcode.com/2020/day/5)
+- **Solution:** [realpython.com](https://realpython.com/python-advent-of-code/#practicing-advent-of-code-day-5-2020)

advent-of-code/solutions/2021/05_hydrothermal_venture/README.md

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+# Day 5, 2021: Hydrothermal Venture
+
+Resources:
+
+- **Puzzle:** [adventofcode.com](https://adventofcode.com/2021/day/5)
+- **Solution:** [realpython.com](https://realpython.com/python-advent-of-code/#practicing-advent-of-code-day-5-2021)