feat(challenge-md): Add initial markdown challenge files

curriculum/challenges/08-coding-interview-prep/project-euler/Problem 79: Passcode derivation.md

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+---
+id: 5900f3bb1000cf542c50fece
+challengeType: 5
+title: 'Problem 79: Passcode derivation'
+---
+
+## Description
+<section id='description'>
+A common security method used for online banking is to ask the user for three random characters from a passcode. For example, if the passcode was 531278, they may ask for the 2nd, 3rd, and 5th characters; the expected reply would be: 317.
+The text file, keylog.txt, contains fifty successful login attempts.
+Given that the three characters are always asked for in order, analyse the file so as to determine the shortest possible secret passcode of unknown length.
+</section>
+
+## Instructions
+<section id='instructions'>
+
+</section>
+
+## Tests
+<section id='tests'>
+
+```yml
+- text: <code>euler79()</code> should return 73162890.
+  testString: 'assert.strictEqual(euler79(), 73162890, "<code>euler79()</code> should return 73162890.");'
+
+```
+
+</section>
+
+## Challenge Seed
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+function euler79() {
+  // Good luck!
+  return true;
+}
+
+euler79();
+```
+
+</div>
+
+
+
+</section>
+
+## Solution
+<section id='solution'>
+
+```js
+// solution required
+```
+</section>