docs: refactor contributing guidelines - add docs guidelines

docs/DOCS_GUIDELINES.MD

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+# Documentation guidelines
+
+## Best practices
+
+- Check the spelling and grammar, even if you have to copy and paste from an external source.
+- Use simple sentences. Easy-to-read sentences mean the reader can quickly use the guidance you share.
+- Try to express your thoughts in a concise and clean way.
+- Either Leave a space or use a `-` between the acronyms ADR and ICS and the corresponding number (e.g. ADR 008 or ADR-008, and ICS 27 or ICS-27).
+- Don't overuse `code` format when writing in plain English.
+- Follow Google developer documentation [style guide](https://developers.google.com/style).
+- Check the meaning of words in Microsoft's [A-Z word list and term collections](https://docs.microsoft.com/en-us/style-guide/a-z-word-list-term-collections/term-collections/accessibility-terms) (use the search input!).
+- We recommend using RFC keywords in user documentation (lowercase). The RFC keywords are: "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL. They are to be interpreted as described in [RFC 2119](https://datatracker.ietf.org/doc/html/rfc2119).
+
+### Links
+
+**NOTE:** Strongly consider the existing links (both within this directory and to the website docs) when moving or deleting files.
+
+Relative links should be used nearly everywhere, due to versioning. Note that in case of page reshuffling, you must update all links references.
+
+### Code snippets
+
+Code snippets can be included in the documentation using normal Markdown code blocks. For example:
+
+```md
+    ```go
+    func() {}
+    ```
+```
+
+It is also possible to include code snippets from GitHub files by referencing the files directly (and the line numbers if needed). For example:
+
+```md
+    ```go reference
+    https://github.com/cosmos/ibc-go/blob/v5.0.0/modules/core/04-channel/keeper/handshake.go#L18-L65
+    ```
+```
+
+## Technical writing course
+
+Google provides a free [course](https://developers.google.com/tech-writing/overview) for technical writing.