Create CONTRIBUTING.md

Signed-off-by: Gerald Venzl <gerald.venzl@oracle.com>

Author: gvenzl

CONTRIBUTING.md

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+# Welcome to Oracle SQL Features contributing guide
+
+Thank you for investing your time in contributing to our project! Any contribution you make will be reflected on [oracle-sql-features.github.io](https://oracle-sql-features.github.io).
+
+In this guide, you will get an overview of the contribution workflow from opening an issue, creating a PR, reviewing, and merging the PR.
+
+## Getting started
+
+To get an overview of the project, please read the [README](README.md).
+
+### Issues
+
+#### Create a new issue
+
+If you spot a problem, please first [search if an issue already exists](https://docs.github.com/en/github/searching-for-information-on-github/searching-on-github/searching-issues-and-pull-requests#search-by-the-title-body-or-comments).
+If a related issue doesn't exist yet, you can [open a new issue](https://github.com/oracle-sql-features/oracle-sql-features.github.io/issues/new).
+If you find a related issue, please comment that you also encountered this error, this will help us weigh the severity of issues and to prioritize them accordingly.
+
+#### Solve an issue
+
+Scan through our [existing issues](https://github.com/oracle-sql-features/oracle-sql-features.github.io/issues) to find one that interests you.
+If you find an issue to work on, you are welcome to open a PR with a fix.
+
+### Make Changes
+
+All source pages are organized in the [features](features) folder.
+All files are in [AsciiDoc](https://asciidoc.org/) format, see the [AsciiDoc Syntax Quick Reference](https://docs.asciidoctor.org/asciidoc/latest/syntax-quick-reference/) for more information on the syntax.
+
+#### Make changes in the UI
+
+Click **Make a contribution** at the bottom of any page to make small changes such as a typo, sentence fix, or a broken link.
+This takes you to the `.adoc` file where you can make your changes and [create a pull request](#pull-request) for a review.
+
+### Commit your update
+
+Commit and **sign-off** the changes once you are happy with them.
+
+### Pull Request
+
+When you're finished with the changes, create a pull request, also known as a PR.
+- Don't forget to [link PR to issue](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue) if you are solving one.
+- Enable the checkbox to [allow maintainer edits](https://docs.github.com/en/github/collaborating-with-issues-and-pull-requests/allowing-changes-to-a-pull-request-branch-created-from-a-fork) so the branch can be updated for a merge.
+Once you submit your PR, a team member will review your proposal. We may ask questions or request additional information.
+- We may ask for changes to be made before a PR can be merged, either using [suggested changes](https://docs.github.com/en/github/collaborating-with-issues-and-pull-requests/incorporating-feedback-in-your-pull-request) or pull request comments.
+You can apply suggested changes directly through the UI. You can make any other changes in your fork, then commit them to your branch.
+- As you update your PR and apply changes, mark each conversation as [resolved](https://docs.github.com/en/github/collaborating-with-issues-and-pull-requests/commenting-on-a-pull-request#resolving-conversations).
+- If you run into any merge issues, check out this [git tutorial](https://github.com/skills/resolve-merge-conflicts) to help you resolve merge conflicts and other issues.
+
+### Your PR is merged!
+
+Congratulations! :tada::tada: The team thanks you :sparkles:.
+
+Once your PR is merged, your contributions will be publicly visible on the [oracle-sql-features.github.io](https://oracle-sql-features.github.io).