RFR: 7832: Refresh dev guide

Tue Jun 28 14:35:17 UTC 2022

**Changes**
* Update the style of interface navigation for easier readability (like _Preferences | Java ..._).
* Mentioned the compiler language level, Eclipse may default to a higher level like 17 and results in IAE (`Unsupported class file major version` / `Incompatible class version`)
* I believe the minimum version needed is now 2021-06 ?

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Commit messages:
 - Refresh dev guide

Changes: https://git.openjdk.org/jmc/pull/404/files
 Webrev: https://webrevs.openjdk.org/?repo=jmc&pr=404&range=00
  Issue: https://bugs.openjdk.org/browse/JMC-7832
  Stats: 19 lines in 2 files changed: 6 ins; 0 del; 13 mod
  Patch: https://git.openjdk.org/jmc/pull/404.diff
  Fetch: git fetch https://git.openjdk.org/jmc pull/404/head:pull/404

PR: https://git.openjdk.org/jmc/pull/404