Fixing a few broken URLs from older PRs

[quintessence]

Description of the change
Fixing broken URLs that were fixed in other open PRs. See list.

Which issue this PR fixes

• PR Fix broken links #240
• PR Add node registration entry alias example #231
• PR adding further description of KeyManager #285

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[quintessence]

For this PR - can we squash the commit since it pulled in a duplicate of the same HeadBucket commit. I'll delete and re-create my fork after, something weird must've happened when I tried to sync my fork.

[sanderson042]

In git terms, "squash the commits" means to combine multiple commits into one commit. It doesn't mean to delete a commit. I think the safest course here is to close this PR and try one more time.

Before starting the new branch for the new PR, be sure to set the working branch to main (git checkout master) and do git pull upstream master (or an equivalent using your git tool of choice). Then create your new branch and recreate these changes on that branch. Publish the new branch as a draft and make sure that pesky old commit doesn't show up. If it's good, then convert the draft PR to a real PR by clicking Ready For Review in GitHub.

[quintessence]

Got it - I'm going to go ahead and try to repair my fork then - issues got worse when I used the "sync fork feature" which had unintended consequences. I'll also delete PR #300 and I'll make both these in one PR for simplicity in the next one.