Job Board: add links to other job boards?

[cmaimone]

Would be good to add a few links to the bottom of the job board to other places with a large number of RSE jobs:

• https://carpentries.topicbox.com/groups/opportunities
• https://academicdatascience.org/jobs
• https://society-rse.org/careers/vacancies/

[danielskatz]

Can we get them to link to us too?

[vsoch]

Adding this to the new site PR right now:

And post-live we can ping the others to be added there (and then this issue will be resolved).

[vsoch]

Done https://us-rse.org/jobs/