Website: Miscellaneous style and content tweaks

[reb-dev]

This PR contains a number of small style and content tweaks to the website.

• Added discord and npm links to the website footer
• Updated the front matter title for intro contribution doc (was previously not title case)
• Docs sidebar: Made only the subsection labels within the Component Reference section collapsible (looks cleaner & is consistent with the rest of the website)
• Removed the 130% increase in font size for larger screens
• Fixed an issue where Stackblitz button would overlap tab labels when screen width was in the range 700px - 729px

Also some changes to the README:

• Added @lee00678 in our maintainers list
• Updated the contributors section

[lee00678]

I wonder if we could benefit having more people joining discord channel by adding the icon here as well:

Just a thought.

[rokotyan]

@lee00678 I think we should add Discord there as well