RFR: 7903058: Add link to pre-built jtreg binaries

[Severin Gehwolf]

Preview here:
https://github.com/jerboaa/jtreg/tree/add-links-to-builds

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Commit messages:
 - 7903058: Add link to pre-built jtreg binaries

Changes: https://git.openjdk.java.net/jtreg/pull/41/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jtreg&pr=41&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7903058
  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jtreg/pull/41.diff
  Fetch: git fetch https://git.openjdk.java.net/jtreg pull/41/head:pull/41

PR: https://git.openjdk.java.net/jtreg/pull/41