Taking up inputs from qr code use cases (#35)

Inclusion of the bvg-digital proposals regarding qr-code/compact
statement:
- Adding timestamps
- Reclassification of required/optional attributes
- Removal of all optional attributes

Renaming resource statement-for-qr-code to compact-statements and moving
definition from paths to components.

Adding contributing guidelines.

CONTRIBUTING.md

@@ -0,0 +1,46 @@
+# Contributing Guidelines
+
+*All forms of contribution (i.e. raising issues and preparing pull requests) to the SFTI community is very welcome and highly appreciated!*
+
+### Contents
+- [First-time Contribution](#first-time-contribution)
+- [How To Contribute](#how-to-contribute)
+- [SFTI Guidelines and Coding Style](#sfti-guidelines-and-coding-style)
+
+
+> **This guide serves to set clear expectations for everyone involved within SFTI's pension stream so that we can improve the API specifications together while also creating a welcoming space for everyone to participate. Following these guidelines will help preserve high-quality SFTI specifications and enable smooth and fast integrations supported by the whole SFTI community.**
+
+# First-time contribution
+If you are not yet part of the SFTI community but interested in contributing to the improvement and further development of the SFTI API's, then please follow the process described below.
+
+**1. Request a GitHub account**  
+Send an email to [[email protected]](mailto:[email protected]) and explain your interest to contribute to SFTI API's. SFTI will get in touch with the requestor to clarify next steps.
+
+**2. Onboarding to SFTI and GitHub**  
+Your request will be checked normally within 5 working days. If your request is approved, you will get the information on how to collaborate in GitHub.
+
+**3. Complete GitHub onboarding**  
+After completing the onboarding process, you can access GitHub and start contributing.
+
+**4. Start contributing**  
+Now you are ready to contribute. Please check the process [how to contribute](#how-to-contribute) in the next section.
+
+# How to contribute
+If you are already part of the SFTI community and interested in contributing to the improvement and further development of the pension API's, then please follow the process described below.
+
+**1. Raise an issue**  
+At GitHub raise an [issue](https://github.com/swissfintechinnovations/ca-pension/issues), describe the initial situation and elaborate on the added value of the proposed change/improvement.
+
+**2. Present issue / change request**  
+After a first review by the API stream leads you will be be invited to present and pitch the proposed change/improvement in the next working group meeting of the SFTI community.
+
+**3. Create a pull request**  
+If the working group participants agree to your proposal a pull [request](https://github.com/swissfintechinnovations/ca-pension/pulls) will be created. Depending on the agreement with the stream leads, the pull request is created by you or the stream leads.
+
+**4. Approval of pull request**  
+The pull request will then be presented and discussed in one of the next working group meetings. The participants then decide if the pull request can be approved and implemented (by merging it to the main branch) in one of the next releases.
+
+![contrib](https://github.com/swissfintechinnovations/ca-payment/assets/116151702/4cad55d8-aed0-42cb-a2b6-b956d217fd0f)
+
+# SFTI guidelines and coding style
+At the [SFTI Wiki](https://github.com/swissfintechinnovations/.github/wiki) you can find more information about SFTI's API design principles, collaboration and implementation guidelines. If you contribute on API specifications, please pay special attention to SFTI's [style guide](https://github.com/swissfintechinnovations/.github/wiki/Style-Guide-Common-APIs) and [naming conventions](https://github.com/swissfintechinnovations/.github/wiki/Naming-Conventions). Make sure you are familiar with both guidelines before submitting your pull request, as there are special [GitHub Actions](https://github.com/swissfintechinnovations/.github/wiki/Github-Actions) implemented to check these rules automatically. Pull requests that do not pass all checks cannot be merged in to the main branch.