mention in the readme that we are working on a website transition

[travi]

• moving from jekyll to gatsby both gets us onto tech that current maintainers are more familiar with and aligns to the tech that is the focus of this user group
• the initial goal is to simple switch stacks without burning time/effort making improvements. first parity with the current site, then consider improvments
• mention that, while we know there are parts of the current site that could be improved, we'd rather defer those changes until after the transition to the new site
• link to the project tracker