Wiki improvements, particularly for Linux users

[MestreLion]

At least for Ubuntu 24.04, the instructions in the last part of the Wiki were great, but there is a better (and simpler) alternative. Also that page is missing a section header:

• The last block of Windows / MacOS / Linux instructions is missing an anchored (sub-)title. That page has 3 anchored sub-titles: Using a JRE or JDK with pre-packed JavaFX (the simple way), When you receive an error from a previously installed version of Java (which I believe adds no useful instruction), and the missing one, that starts at the last "For Windows", and could be named "Using a regular JRE or JDK and installing JavaFX separately (the standard way)"
• On the Linux part, it could be mentioned that the system JRE/JDK can be installed with sudo apt install default-jre (or default-jdk). It will already be Java 21 for latest Ubuntu 24.04 LTS, but Java 11 for older releases.
• While Debian and Ubuntu does have an openjfx package on its apt repositories, it is still Java 11, and MCA Selector requires Java 21. So for now it's better not to mention it.
• There is a JavaFX Snap package for latest stable version, currently 23: sudo snap install openjfx. The command line for MCA Selector in this case is similar to the "simple way", just changing the JavaFX path:

java --module-path /snap/openjfx/current/sdk/lib --add-modules ALL-MODULE-PATH -jar mcaselector-*.jar

• Or an alternative mentioned in the snap maintainer repository:

source "$(openjfx)" && java --module-path "$JAVAFX_LIB" --add-modules ALL-MODULE-PATH -jar mcaselector-*.jar

• I've tested it and it works great! So maybe this could be the new "simple way" for Debian/Ubuntu users? In a nutshell:

sudo apt install default-jre && sudo snap install openjfx