Contributing: Add guidelines for contributing docs (#19108)

* Docs: Add docs for how to contribute to docs

* Fix review comments from marefr

* Add information about links on doc pages

docs/sources/contribute/documentation.md

++++
+title = "Documentation"
+description = "Contributing to documentation"
+type = "docs"
+[menu.docs]
+parent = "contribute"
+weight = 2
++++
+
+# Contributing to documentation
+
+## How do I contribute?
+
+If you’re unsure about where to start, check out some of our [open docs issues](https://github.com/grafana/grafana/issues?q=is%3Aopen+is%3Aissue+label%3Atype%2Fdocs).
+
+Sometimes it can be difficult to understand an issue when you're just getting started. We strive to keep a collection of [beginner-friendly issues](https://github.com/grafana/grafana/issues?q=is%3Aopen+is%3Aissue+label%3Atype%2Fdocs+label%3A"beginner+friendly") that is more suitable for first-time contributors.
+
+When you’ve found an issue you want to work on, you’re encouraged to comment on the issue to let other people know you intend to work on it.
+
+If you encounter any misspellings, or violations to the style guide, please let us know by submitting an issue.
+
+On every page in the documentation there are two links:
+
+- __Edit this page__ takes you directly to the file on GitHub where you can contribute a fix.
+- __Request doc changes__ prepares an issue on GitHub with relevant information already filled in.
+
+## Community
+
+If you have questions on a specific issue, post a comment to ask for clarification, or to give feedback.
+
+For general discussions on documentation, you’re welcome to join the `#docs` channel on our [public Grafana Slack](http://slack.raintank.io) team.
+
+## Guidelines
+
+All Grafana documentation is written using [Markdown](https://en.wikipedia.org/wiki/Markdown), and can be found in the [docs](https://github.com/grafana/grafana/tree/master/docs) directory in the [Grafana GitHub repository](https://github.com/grafana/grafana). The [documentation website](https://grafana.com/docs) is generated with [hugo](https://gohugo.io) which uses [Blackfriday](https://github.com/russross/blackfriday) as its Markdown rendering engine.
+
+### Structure
+
+The documentation is organized into topics, called _sections_.
+
+Each top-level section is located under the [docs/sources](https://github.com/grafana/grafana/tree/master/docs/sources) directory. Subsections are added by creating a subdirectory in the directory of the parent section.
+
+For each section, a `_index.md` file is used to provide an overview of the topic.
+
+### Style guide
+
+The [codespell](https://github.com/codespell-project/codespell) tool is run for every change to catch common misspellings.
+
+- "Open source" should be hyphenated when used as an adjective, e.g. _open-source software_. The open form should be preferred when used as a noun, e.g. _Grafana is open source_.
+- Use "data source" instead of "datasource" unless used as an identifier, in code or as part of URLs.
+- Acronyms should be uppercased, e.g. URL, DNS, or TCP/IP.