docs: update testing instructions (#2210)

docs/CONTRIBUTING.md

@@ -175,6 +175,12 @@ This glossary helps to keep terms and their meanings consistent across documenta
 
 ## Documentation Style Guide
 
+Janssen Project documentation uses Markdown. Guidelines below are intended to bring consistency in writing and formatting documents. 
+
+!!! Testing
+
+    [Janssen Project documentation site](https://docs.jans.io) is published using MkDocs. Markdown parsers used by Github and the one used by MkDocs may have slight variations in how they generate HTML. So, for a small number of cases, document may look different between Github and [Janssen Project documentation site](https://docs.jans.io). Hence it is critical to [test documentation](developer/testing.md#documentation-local-testing) changes locally before pushing to repository. This will ensure that final HTML rendering of documents by MkDocs is as desired.
+
 ### General Text
  - Allow long lines to wrap, rather than manually breaking them. For example, the Introduction paragraph is a single line
  - Keep explanations short and clear
@@ -191,6 +197,7 @@ This glossary helps to keep terms and their meanings consistent across documenta
  - Organize the information in the document from least technical to most technical if possible. Start conceptual, then get detailed
 
 ### Lists
+ - Leave a blank line between text and first item in the list
  - Only use a numbered list if the order of the list matters
  - A line of a list should not end with a period. If it's multiple sentences, like this one, drop the last period
  - Start each item in the list with a capital letter
@@ -204,10 +211,13 @@ This glossary helps to keep terms and their meanings consistent across documenta
     1. This is the third item
     ```
 
-It will look like this:
-1. This is the first item
-1. This is the second item
-1. This is the third item
+    It will look like this:
+
+    ```
+    1. This is the first item
+    2. This is the second item
+    3. This is the third item
+    ```
 
  - To include additional lines in a list item, start the sub-line with four spaces. For example:
 

docs/developer/testing.md

@@ -24,11 +24,15 @@ testing.
 Dependency vulnerabilities are monitored by Gihub. In addition we plan to use the [Linux Foundation Community Bridge](https://security.communitybridge.org) vulnerability detection platform.
 
 # Documentation local testing
+
 While contributing documentation to official Janssen Project [documentation](https://jans.io/docs/) it is important to make sure that documents meet [style guidelines](../CONTRIBUTING.md#documentation-style-guide) and have been proofread to remove any typographical or grammatical errors.
 Janssen Project uses [Material for MkDocs](https://squidfunk.github.io/mkdocs-material/) to create the documenation site. Before new content is pushed to the repository on GitHub, it should be tested locally by the author. Author can do this by deploying Material for MkDocs locally.
 
 High-level steps involve:
+
 1. [Install Material for MkDocs](https://squidfunk.github.io/mkdocs-material/getting-started/#installation)
-2. [Preview as you write](https://squidfunk.github.io/mkdocs-material/creating-your-site/#previewing-as-you-write)
+2. Install required plugins
+3. [Preview as you write](https://squidfunk.github.io/mkdocs-material/creating-your-site/#previewing-as-you-write)
+