Add gitignore to exclude unnecessary files from being committed

heroku/.gitignore

@@ -0,0 +1,30 @@
+### Terraform ###
+# Local .terraform directories
+**/.terraform/*
+
+# Crash log files
+crash.log
+
+# REMOVE EVERYTHING THAT FOLLOWS THIS LINE IF YOU ARE NOT USING A REMOTE BACKEND
+# AND PLAN ON COMMITTING YOUR TERRAFORM CONFIGURATION AND STATE TO A GIT REPOSITORY.
+
+# .tfstate files
+*.tfstate
+*.tfstate.*
+
+# Ignore any .tfvars files that are generated automatically for each Terraform run. Most
+# .tfvars files are managed as part of configuration and so should be included in
+# version control.
+#
+# example.tfvars
+
+# Ignore override files as they are usually used to override resources locally and so
+# are not checked in
+override.tf
+override.tf.json
+*_override.tf
+*_override.tf.json
+
+# Include override files you do wish to add to version control using negated pattern
+#
+# !example_override.tf