maint: outline issue reporting, ignore certain files when docker building

Author: mgxd

.dockerignore

@@ -0,0 +1,2 @@
+Dockerfile
+.git/

.github/PULL_REQUEST_TEMPLATE.md

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+### Summary
+<!-- If you are having conversion troubles, please share as much
+relevant information as possible. This includes, but is not limited to:
+- log of conversion
+- heuristic
+-->
+
+
+
+### Platform details:
+
+Choose one:
+- [ ] Local environment
+<!-- If selected, please provide OS and python version -->
+- [ ] Container
+<!-- If selected, please provide container name and tag"-->
+
+- Heudiconv version: <!-- Command: heudiconv --version -->