doc: add sxa as calendar maintainer

Adding myself after a discussion with @richardlau about some potential discrepencies with the current data, potentially as a result of [some meetings moving to LFX](https://github.com/nodejs/admin/issues/1024). Noting that I already have access to zoom as per https://github.com/nodejs/email/blob/8e7172f12f7d4d7507effe35e9893eb3d6897ebb/iojs.org/aliases.json#L215 so this part of helping to assist in hosting project meetings going forward.