Small changes in Markdown component

[murilo-cunha]

Hi, really like the framework!

Used it to build a static website (GH pages), and had to make a few adjustments to the Markdown component and figured I'd submit a PR here.

Summary of changes/commits:

1. Use rehype-raw plugin in react-markdown to omit markdown comments (i.e.: <!-- comment -->)
   1. See react-markdown's issue for more info
2. Use chakra-ui's UnorderedList, OrderedList and ListItem
   1. Otherwise the list was not aligned with the rest of the text
   2. Feel free to drop the last commit if this is not the desired implementation

Thanks!

[picklelo]

Thanks for the changes!