docs: Draft for the Maintaining document (#504)

Signed-off-by: Marcos Iglesias Valle <golodhros@gmail.com>

MAINTAINING.md

+# Maintaining Amundsen
+
+As maintainers of the project, this is our guide. Most of the steps and guidelines
+in the [Contributing](CONTRIBUTING.md) document apply here, including how to set
+up your environment, write code to fit the code style, run tests, craft commits
+and manage branches.
+
+Beyond this, this document provides some details that would
+be too low-level for contributors.
+
+## Table of Contents
+
+- [Communication](#communication)
+- [Managing the community](#managing-the-community)
+- [Workflow](#workflow)
+- [Architecture](#architecture)
+- [Updating the changelog](#updating-the-changelog)
+- [Documentation](#documentation)
+- [Labels](#labels)
+- [Adding new projects](#adding-new-projects)
+- [Related Documents](#related-documents)
+
+## Communication
+
+We have several ways that we can communicate with each other:
+
+- To show our direction and next steps, the [**roadmap**][roadmap] is the best place.
+- To track progress on the movement of issues, [**labels**](#labels)
+  are useful.
+- To learn about what the community has been working lately, our [community meeting] is a great event. It happens the first Thursday of every month at 9AM PST, and you can watch past meeting recordings [here][cmeetingrecordings]
+- To chat with the maintainers team, get support or connect with Amundsen's community, join our Slack
+
+[roadmap]: https://www.amundsen.io/amundsen/roadmap/
+[cmeeting]: meet.google.com/mqz-ndck-jmj
+[cmeetingrecordings]: https://www.youtube.com/channel/UCgOyzG0sEoolxuC9YXDYPeg
+[slack]: amundsenworkspace.slack.com
+
+## Managing the community
+
+We try to create and foster a community around Amundsen. We do this by:
+
+- Answering questions from members of the community
+- Triaging Github issues, adding the proper [labels][labels] to new tickets
+- Closing stale issues and feature requests
+- Keeping the community informed by ensuring that we add communications regularly with the new features
+- Ensuring that the documentation, as well as the documentation site, is kept up to
+  date
+- Doing code reviews for other maintainers and the community
+- Reviewing [RFCs][rfcs] and shaping the future of the project
+
+[labels]: https://github.com/amundsen-io/amundsen/labels
+[rfcs]: https://github.com/amundsen-io/rfcs
+
+## Workflow
+
+We generally follow [GitHub Flow]. The `master` branch is the main line, and all
+branches are cut from and get merged back into this branch. Generally, the
+workflow is as follows:
+
+[github flow]: https://help.github.com/articles/github-flow/
+
+- Cut a feature or bugfix branch from this branch
+- Upon completing a branch, create a PR and ask another maintainer to approve
+  it
+- Try to keep the commit history as clean as possible. Before merging, squash
+  "WIP" or related commits together and rebase as needed
+- Once your PR is approved, and you've cleaned up your branch, you're free to
+  merge it in
+
+## Architecture
+
+We have covered Amundsen's architecture in our [docs](https://lyft.github.io/amundsen/architecture/).
+
+## Documentation
+
+We use [mkdocs] for creating our documentation from Markdown files. This system is configured from the 'mkdocs.yml' file in the root of this repository.
+
+Currently, our docs are built and deployed automatically with a GitHub action, so we shouldn't need to do anything.
+
+[mkdocs]: https://www.mkdocs.org/
+
+## Labels
+
+We've found labels to be useful for cataloging and marking progress on features and bugs. You can read about our labels on the [issue_labeling](https://lyft.github.io/amundsen/issue_labeling/) document.
+
+## Adding new projects
+
+To add new projects to the amundsen-io organization, we will first discuss it through a GitHub issue. Once we discuss it thoroughly (~3-5 business days, depending on the volume of conversation), the maintainers will decide whether the new project should be added.
+
+## Related Documents
+
+- [Contributing Guide](https://www.amundsen.io/amundsen/CONTRIBUTING/)
+- [Governance Document](https://github.com/amundsen-io/amundsen/blob/master/GOVERNANCE.md)