Added TECH_DEBT.md document

[Sandervanmaurik]

What

Adds TECH_DEBT document to keep track of technical debt.

Why

Explain why these things are changes. This explanation is for your colleagues and your future self.

Code Review

Please consider the following checklist when reviewing this Pull Request.
More background and details here.

• [ ] Does the code actually solve the problem it was meant to solve?
• [ ] Is the code covered by unit tests? Integration tests?
• [ ] Does anything here need documentation? (Focus on why, not what.)
• [ ] Does any of this code deal with privacy sensitive information or affects security? Ask an additional reviewer.
• [ ] Is the code easy to understand and change in the future?
• [ ] Is the same code or concept duplicated? Find a balance between DRYness and readability.
• [ ] Does the code reasonably adhere to the Kabisa coding standards?
• [ ] Be kind.

[codeclimate[bot]]

Code Climate has analyzed commit d1e9c624 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 19.0% (0.0% change).

View more on Code Climate.