Markdown guide for the handbook (#6864)

* Markdown guide for the handbook

Markdown guide for the handbook.

* Update markdown-guide.md

* Update markdown-guide.md

* Update markdown-guide.md

* Update markdown-guide.md

* Update markdown-guide.md

* Update handbook/digital-experience/README.md

* Update handbook/digital-experience/markdown-guide.md

* Handbook - Re-ordered Digital Experience README.md

- I repositioned Markdown to be under Voice and tone.
@Desmi-Dizney, I think you are right. Including the Markdown section under the section for writers is better.

* Update markdown-guide.md

- actioned review comments (https://github.com/fleetdm/fleet/pull/6864#pullrequestreview-1053545929)
- reformatted the markdown guide.
- updated nested list examples to display inside a table
- removed a couple of link examples that don't currently render on the website

* Update README.md

- I removed the Markdown section. I'd prefer to link to this guide as and when it's needed.

Co-authored-by: Desmi-Dizney <99777687+Desmi-Dizney@users.noreply.github.com>

handbook/digital-experience/markdown-guide.md

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+# Markdown guide
+
+## Headings
+
+Try to stay within three or four heading levels. Complicated documents may use more, but pages with a simpler structure are easier to read.
+
+| Markdown | Rendered heading |
+|:--------------------|:-----------------------------|
+| `# Heading 1` | <h1>Heading 1</h1> |
+| `## Heading 2` | <h2>Heading 2</h2> |
+| `### Heading 3` | <h3>Heading 3</h3> |
+| `#### Heading 4` | <h4>Heading 4</h4> |
+
+## Emphasis
+
+| Markdown | Rendered text |
+|:--------------------|:-----------------------------|
+| `**Bold**` | <strong>Bold</strong> |
+| `*Italic*` | <em>Italic</em> |
+| `***Bold italic***` | <em><strong>Bold italic</strong></em> |
+| `~~Strikethrough~~` | <s>Strikethrough</s> |
+
+## Lists
+
+### Ordered lists
+
+| Markdown | Rendered list |
+|:-------------|:-----------------------------|
+| <pre>1. Line one<br>2. Line two  <br>3. Line three<br>4. Line four</pre> | 1. Line one<br>2. Line two<br> 3. Line three<br>4. Line four |
+| <pre>1. Line one<br>1. Indent one<br>2. Line two<br>3. Line three<br>1. Indent one<br>2. Indent two<br>4. Line four</pre> | 1. Line one<br>&nbsp;1. Indent one<br>2. Line two<br>3. Line three<br>&nbsp;1. Indent one<br>&nbsp;2. Indent two<br>4. Line four |
+
+### Unordered lists
+
+| Markdown | Rendered list |
+|:-------------|:-----------------------------|
+| <pre>- Line one<br>- Line two  <br>- Line three<br>- Line four</pre> | - Line one<br>- Line two<br>- Line three<br>- Line four |
+| <pre>- Line one<br> - Indent one<br>- Line two<br>- Line three<br> - Indent one<br> - Indent two<br>- Line four</pre> | - Line one<br>&nbsp;- Indent one<br>- Line two<br>- Line three<br>&nbsp;- Indent one<br>&nbsp;- Indent two<br>- Line four |
+
+## Links
+
+The Fleet website currently supports the following Markdown link types.
+
+### Inline link
+
+It's a classic.
+
+#### Example
+
+`[This is an inline link](https://domain.com/example.md)`
+
+#### Rendered output
+
+[This is an inline link](https://domain.com/example.md)
+
+### Link with a tooltip
+
+Adding a tooltip to your link is a great way to provide additional information.
+
+#### Example
+
+`[This is link with a tooltip](https://domain.com/example.md "You're awesome!")`
+
+#### Rendered output
+
+[This is link with a tooltip](https://domain.com/example.md "You're awesome!")
+
+### URLs
+
+Add angle brackets "< >" around a URL to turn it into a link.
+
+#### Example
+
+`<https://fleetdm.com>`
+
+#### Rendered output
+
+<https://fleetdm.com>
+
+### Emails
+
+To create a mailto link... oh wait, I'm not going to tell you.
+
+> **Important**: To avoid spam, we **NEVER** use mailto links.
+
+## Tables
+
+To create a table, start with the header by separating rows with pipes (" | ").
+Use dashes (at least 3) to separate the header, and add colons to align the text in the table columns.
+
+#### Example
+
+```
+| Category one | Category two | Category three |
+|:---|---:|:---:|
+| Left alignment | Right alignment | Center Alignment |
+```
+
+#### Rendered output
+
+| Category one | Category two | Category three |
+|:---|---:|:---:|
+| Left alignment | Right alignment | Center Alignment |
+
+<meta name="maintainedBy" value="mike-j-thomas">
+<meta name="title" value="Markdown-guide">