SEO/meta data for individual pages

## Feature request
The ability to add custom meta title and description to pages in addition of the globally defined `SiteMetadata`

**What is the expected behavior?**
Being able to add custom meta title/description to a page, overriding the globally set information

**What is motivation or use case for adding/changing the behavior?**
Improve SEO. The same title and description is found on every page

**How should this be implemented in your opinion?**
Perhaps this could be set in the markdown, under a `meta` section

**Are you willing to work on this yourself?**
yes if I have some guidance