docs: add contributing and issue templates

.github/CONTRIBUTING.md

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+# Contributing to Ghost-CLI
+
+Welcome to the Ghost-CLI project, and thank you for wanting to get started contributing!
+
+To setup Ghost-CLI for development, please read through the developer setup in the [readme](../README.md).
+
+Read through the list of [open issues](https://github.com/TryGhost/Ghost-CLI/issues), and if you find one that you want to work on, please comment on it so that others will know it's being worked on 😉
+
+Once you've implemented the feature or fixed the issue, please make sure:
+
+- it passes tests (`yarn test`)
+- all commits are squashed into one or two commits
+- the commit message follows [this format](https://github.com/conventional-changelog/standard-version#commit-message-convention-at-a-glance)
+
+Then submit a PR and one of the core team will review it!
+
+If you have any questions, feel free to drop by our [slack channel](https://slack.ghost.org)! We'd be happy to help 😄
+
+#### Note: If you wish to implement a new feature, it would be wise to open an issue about it beforehand. That way the Core Team can make comments and ensure that the feature is in the best interests and direction of the CLI.
+
+## Contributor License Agreement
+
+By contributing your code to Ghost you grant the Ghost Foundation a non-exclusive, irrevocable, worldwide, royalty-free, sublicenseable, transferable license under all of Your relevant intellectual property rights (including copyright, patent, and any other rights), to use, copy, prepare derivative works of, distribute and publicly perform and display the Contributions on any licensing terms, including without limitation: (a) open source licenses like the MIT license; and (b) binary, proprietary, or commercial licenses. Except for the licenses granted herein, You reserve all right, title, and interest in and to the Contribution.
+
+You confirm that you are able to grant us these rights. You represent that You are legally entitled to grant the above license. If Your employer has rights to intellectual property that You create, You represent that You have received permission to make the Contributions on behalf of that employer, or that Your employer has waived such rights for the Contributions.
+
+You represent that the Contributions are Your original works of authorship, and to Your knowledge, no other person claims, or has the right to claim, any right in any invention or patent related to the Contributions. You also represent that You are not legally obligated, whether by entering into an agreement or otherwise, in any way that conflicts with the terms of this license.
+
+The Ghost Foundation acknowledges that, except as explicitly described in this Agreement, any Contribution which you provide is on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING, WITHOUT LIMITATION, ANY WARRANTIES OR CONDITIONS OF TITLE, NON-INFRINGEMENT, MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE.

.github/ISSUE_TEMPLATE.md

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+Welcome to Ghost-CLI's GitHub repo! 👋🎉
+
+Do you need help or have a question? Please come chat in Slack: https://slack.ghost.org/ 👫.
+
+### This issue is a
+
+* [ ] Bug Report
+* [ ] Feature Request
+
+### Summary
+
+If this is a bug, double-check and make sure there's not already an existing issue for it, then provide a quick summary of what error is occurring.
+
+If this is a feature request, use this section to describe what feature you would like to see in the CLI, as well as a quick summary of any benefits or drawbacks you can think of if this feature is implemented.
+
+### Steps to Reproduce (for a bug report)
+
+1. This is the first step
+2. This is the second step, etc.
+
+Any other info e.g. Why do you consider this to be a bug? What did you expect to happen instead?
+
+Also, if there is a log file generated (the CLI will output a message saying "Additional Log Info can be found at..."), please paste the contents of that log file here.
+
+### Technical details (will be automatically output by Ghost-CLI if an error occurs):
+
+* OS: 
+* Node Version:
+* Ghost-CLI Version: 
+* Environment: 
+* Command: