RFR: Added QuickLink boxes

[Jesper Wilhelmsson]

The intention with the QuickLink boxes is that experienced developers who only want to find the right technical page should be able to do so without having to browse the text.

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Commit messages:
 - Added QuickLink boxes

Changes: https://git.openjdk.java.net/guide/pull/34/files
 Webrev: https://webrevs.openjdk.java.net/?repo=guide&pr=34&range=00
  Stats: 33 lines in 2 files changed: 28 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/guide/pull/34.diff
  Fetch: git fetch https://git.openjdk.java.net/guide pull/34/head:pull/34

PR: https://git.openjdk.java.net/guide/pull/34