Problem: candidates need guidance to share their application

[zolotokrylin]

Problem

Candidates who open a job application have no prompt to share it or collect
reactions. The follow-up comment still instructs them to submit a profile PR
rather than rallying their network, so the viral mechanic is inert for all
existing and new applicants.

Solution

Update job-application-follow-up-body.md to replace the profile PR
instructions with a sharing prompt:

Your application is now public — share it with your network and ask them to
react with 👍. The more support you collect, the higher you rank on the
leaderboard and the sooner you get reviewed.
Your application: https://github.com/holdex/trial/issues/${issue_number}