Add space before hyphen so the assignee mention resolves

[ale210]

One character. Part of #155.

Problem

The reminder greeting is Hello ${assignees}-, which renders as Hello @username-. GitHub does not parse that as a mention. The hyphen is a legal username character so the parser consumes it, and since a username cannot end in a hyphen the whole match fails — no link, and no mention notification.

Verified against GitHub's own renderer (POST /markdown, mode gfm):

Text	Rendered
@ExperimentsInHonesty-	no mention link
@ExperimentsInHonesty -	mention link
@ExperimentsInHonesty,	mention link
@ExperimentsInHonesty!	mention link

With more than one assignee only the last is affected — @a, @b- produces one link instead of two.

Visible in the first live run: the comment on #158 shows Hello @ExperimentsInHonesty- as plain text.

Assignees still receive a subscriber notification because they are assigned, so this is not silent — but the reminder is not actually tagging anyone, which is most of its purpose.

Fix

Hello ${assignees}- → Hello ${assignees} - in add-update-instructions-template.md.

Re-rendered after the change: one user-mention link, as expected.

Note

This comes from automate-the-org's shipped template, so hackforla/website and hackforla/tdm-calculator have the same broken greeting in their installed copies, and any new install will too until the upstream example is fixed. Deliberately out of scope here.