feat(challenges): add find-closest-number

challenges/find-closest-number/README.md

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+# find-closest-number
+
+Created by [@Divlo](https://github.com/Divlo) on 1 May 2022.
+
+## Instructions
+
+Given an array of `n` integers, find the closest value to the given number (`given_number`).
+
+## Input
+
+- **Line 1:** An integer `given_number` for the number to find the closest value to
+- **Line 2:** An integer `n` for the length of the list of integers
+- **`n` next lines:** the integers
+
+## Output
+
+The closest value in the array to the given number.
+
+## Examples
+
+See the `test` folder for examples of input/output.
+
+### Example 1
+
+#### Input
+
+```txt
+3
+6
+1
+2
+3
+4
+5
+6
+```
+
+#### Output
+
+```txt
+3
+```
+
+**Explanation:** The given number is `3` and `3` is in the array, so the closest value is `3`.
+
+### Example 2
+
+#### Input
+
+```txt
+0
+14
+7
+-10
+13
+8
+4
+-7
+-12
+-3
+3
+-9
+6
+-1
+-6
+7
+```
+
+#### Output
+
+```txt
+-1
+```