add probot: welcome

.github/config.yml

@@ -0,0 +1,11 @@
+newIssueWelcomeComment: >
+  Hi there!
+  
+  Thanks a bunch for opening your first issue! :pray:
+  As you're new to this repo, we'd like to suggest that you read our [code of conduct](https://github.com/containrrr/watchtower/blob/master/CODE_OF_CONDUCT.md)
+  
+newPRWelcomeComment: >
+  Thanks for opening this pull request! Please check out our [contributing guidelines](https://github.com/containrrr/watchtower/blob/master/CONTRIBUTING.md) as well as our [code of conduct](https://github.com/containrrr/watchtower/blob/master/CODE_OF_CONDUCT.md).
+
+firstPRMergeComment: >
+  Congrats on merging your first pull request! We are all very proud of you! :sparkles: