add enhancement request issue template (#75)

.github/ISSUE_TEMPLATE/enhancement.md

@@ -0,0 +1,22 @@
+---
+name: Enhancement Request
+about: Suggest an enhancement to the Lens application
+
+---
+<!-- Please only use this template for submitting enhancement requests -->
+<!--
+    Check already existing enhancement request on this list: https://github.com/kontena/lens/issues?q=is%3Aissue+is%3Aopen+label%3Aenhancement
+    If similar request already exists, please add comments on the existing issue.
+-->
+
+**What would you like to be added**:
+
+
+**Why is this needed**:
+
+
+**Environment you are Lens application on:**
+
+- Kubernetes distribution: [EKS, AKS, GKE, Rancher, ...]
+- Desktop OS: <the OS Lens app runs on in your case>
+