Added a template for adding new puzzles as "issues"

Author: akalai

.github/ISSUE_TEMPLATE/new-puzzle.md

@@ -0,0 +1,33 @@
+---
+name: New puzzle
+about: Create your own puzzle by defining a function
+title: New puzzle
+labels: New-puzzle
+assignees: akalai
+
+---
+
+```python
+def sat(x: str): 
+    """optional problem description"""
+    return "Hello " + x == "Hello world"   # change this to your puzzle
+```
+
+Solution hidden below so that other people can try to solve it.
+<details><summary>Reveal solution</summary>
+
+```python
+def sol():
+    return "world"  # replace with your solution
+```
+</details>
+
+Please post your solutions to this puzzle in the comments using the following formatting:
+````
+<details><summary>Reveal solution</summary>
+```python
+def sol():
+    return "world"  # replace with your solution
+```
+</details>
+````