Rename program -> solution

Author: Arxcis

README.md

@@ -3,14 +3,14 @@ Solving the 2020 edition of https://adventofcode.com/ in many languages, and tes
 
 ## Contributing
 1. Make a branch. Example: `git checkout -b jonas/day-03`
-2. Write a program, in the language of your choice. Example: `vim day-03/solution/super-optimized.py`
-3. Test your program.
+2. Write a solution, in the language of your choice. Example: `vim day-03/solution/super-optimized.py`
+3. Test your solution.
 
 ```sh
 cat day-03/input | python3 day-03/solution/super-optimized.py | diff - day-03/output
 ```
 
-4. Make sure your program is automatically tested by the Github CI, by adding a line of code to `day-03/test.sh`.
+4. Make sure your solution is automatically tested by the Github CI, by adding a line of code to `day-03/test.sh`.
 *Example line:*
 ```sh
 $DIR/../scripts/test-py.sh $DIR "solution/super-optimized.py"
@@ -19,13 +19,13 @@ $DIR/../scripts/test-py.sh $DIR "solution/super-optimized.py"
 5. Make a Pull Request to the `main` branch.
 6. Merge when the tests pass!
 
-**How are programs tested?**
+**How are solutions tested?**
 
-Every program gets the `input`-challenge delivered to `stdin`, and every program is expected to answer, by writing the `output`-answer to `stdout`.
+Every solution gets the `input`-challenge delivered to `stdin`, and every solution is expected to answer, by writing the `output`-answer to `stdout`.
 
 ```sh
 #!/bin/bash
-cat input | <run-program> | diff - output
+cat input | <run-solution> | diff - output
 ```
 
 **The CI does not support my favourite language. What do I do?**