Update/Improve Eclipse installation instructions
Reduce mistakes for installing eTrice
- Add instruction for non-official Eclipse installation ** Hint for JustJ17 "complete not-stripped" version ** Add JustJ as optional dependency ? ** mention CubeIDE explicitly ?
- Update hint "... use Eclipse 2020-09 or later with Java 11+ to avoid any installation issues". 2020 is too old, using Java 22 causes issues. How to keep the hint up to date ?
- Update install documentation ** screenshot is showing nightly as update site, better change to a release https://eclipse.dev/etrice/documentation ** add instruction to update Java via JustJ
- Idea: add update site for latest release