Add support for Jekyll Relative Links

[dellagustin]

Reasoning

When pages are generated from Markdown content, users (including me) expect that links to relative md files (i.e. [some text](./other-file.md) will automatically be converted to links to the rendered page corresponding to the linked file.

Turns out that Jekyll does not support this out of the box.

Consequence

Without support for relative linking to other files, there are two options:

• Hard code the link to the resulting page: https://github.com/InnerSourceCommons/innersourcecommons.org/blob/c7455d7fc2a5190552a7d9b8d86cce6b0a19863b/events/isc-spring-2020.md#11
• Use a format that will be rendered correctly, but will not work on the markdown file (i.e. the rendered Markdown on github, or when using an editor such as vscode)
  https://jekyllrb.com/docs/liquid/tags/#linking-to-posts
  https://stackoverflow.com/questions/4629675/jekyll-markdown-internal-links

Proposed solution

Add the Jekyll Relative Links

[rrrutledge]

That's a great idea! It looks like it's supported by GitHub pages, too!