[MRG] Add github issue template message

.github/issue_template.md

@@ -0,0 +1,44 @@
+#### Description
+<!-- Describe your issue here.-->
+
+#### Steps/Code to Reproduce
+<!-- Please provide a **minimal** highlighted code example for
+reproduction. (See https://help.github.com/articles/creating-and-highlighting-code-blocks/
+for code blocks highlighting, and https://stackoverflow.com/help/mcve
+for what is a minimal reproducible code.)
+
+Example:
+```python
+from metric_learn import NCA
+from sklearn.datasets import make_classification
+from sklearn.utils import check_random_state
+
+X, y = make_classification(random_state=0)
+nca = NCA()
+nca.fit(X, y)
+```
+If the code is too long, feel free to put it in a public gist and link
+it in the issue: https://gist.github.com
+-->
+
+#### Expected Results
+<!-- Example: No error is thrown. Please paste or describe the expected results.-->
+
+#### Actual Results
+<!-- Please paste or specifically describe the actual output or traceback. You can use ```ptb for python traceback formatting-->
+
+#### Versions
+<!-- Please run the following snippet and paste the output below.
+
+import platform; print(platform.platform())
+import sys; print("Python", sys.version)
+import numpy; print("NumPy", numpy.__version__)
+import scipy; print("SciPy", scipy.__version__)
+import sklearn; print("Scikit-Learn", sklearn.__version__)
+import metric_learn; print("Metric-Learn", metric_learn.__version__)
+
+(If the last statement returns "AttributeError: 'module' object has no attribute '__version__'", you can instead run this in a terminal:
+$ pip show metric_learn | grep Version
+)
+-->
+<!-- Thanks for contributing! -->