add new issue template for new simulariumio converter requests (#196)

Author: ascibisz

.github/ISSUE_TEMPLATE/converter_request.md

@@ -0,0 +1,16 @@
+---
+name: New Converter Request
+about: '"I would like to visualize x in Simularium"'
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+## Simulation Engine Details
+
+_Please provide information about the simulation you would like to visualize in Simularium._
+
+## Documentation and Example Data
+
+_Please provide any links to documentation about the simulation engine and any helpful example data_