Adding multi-echo posters and presentations

[handwerkerd]

We will use this repository as a place to centralize multi-echo related content at OHBM 2023. In addition to going through the abstract site to identify content to include here (any volunteers?), if you have content you want included, submit a pull request or comment on this issue. Content can include a link to a poster/presentation or, if you have an interactive demo or other site, we can also link to that directly from here.