Add _become a contributor_ issue template (#63)

Author: fcollonval

.github/ISSUE_TEMPLATE/become-a-contributor.md

@@ -0,0 +1,16 @@
+---
+name: Become a contributor
+about: Become a member of this organization and contributor of a project.
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+<!-- Thanks a lot for proposing your help -->
+<!-- Would you mind sharing some information about you and your contributor goals -->
+
+I'm ... <!-- this is optionally, feel free to remove this paragraph if it makes you uncomfortable -->
+
+I would like to contribute to the repository ...
+In particular I would like to <!-- add a awesome feature, fix a bug I'm facing,... -->