chore: add config for welcome bot (Azure#296)

.github/config.yml

@@ -0,0 +1,24 @@
+# Configuration for new-issue-welcome - https://github.com/behaviorbot/new-issue-welcome
+
+# Comment to be posted to on first time issues
+newIssueWelcomeComment: >
+  👋 Thanks for opening your first issue here! If you're reporting a 🐞 bug, please make sure you include steps to reproduce it.
+
+# Configuration for new-pr-welcome - https://github.com/behaviorbot/new-pr-welcome
+
+# Comment to be posted to on PRs from first time contributors in your repository
+newPRWelcomeComment: >
+  💖 Thanks for opening your first pull request! 💖
+  We use [semantic commit messages](https://www.conventionalcommits.org/en/v1.0.0-beta.2/) to streamline the release process. Before your pull request can be merged, you should **make sure your first commit and PR title** start with a semantic prefix.
+  Examples of commit messages with semantic prefixes:
+  - `fix: change azure disk cachingMode to ReadOnly`
+  - `feat: make maximumLoadBalancerRuleCount configurable`
+  - `docs: add note on AKS-Engine and AKS relationship`
+  
+  Make sure to check out the [developer guide](https://github.com/Azure/aks-engine/blob/master/docs/community/developer-guide.md) for guidance on testing your change.
+
+# Configuration for first-pr-merge - https://github.com/behaviorbot/first-pr-merge
+
+# Comment to be posted to on pull requests merged by a first time user
+firstPRMergeComment: >
+  Congrats on merging your first pull request! 🎉🎉🎉