Add one-liner to execute install_mcl.sh

[rheitjoh]

Currently, the user has to download install_mcl.sh to execute it. It should be possible to automate this process by using curl or wget to download install_mcl.sh and then execute it via a one-liner bash command that can just be pasted into a terminal. This should be included in the readme.

[rheitjoh]

Ok, this may not be so simple since the user has to provide their Java include path to the install script.

[JanBobolz]

The script could best-effort try out a few typical locations (including environment variables like $JAVA_HOME and /usr/libexec/java_home on macOS and such) and fall back to user input in the worst case.

Though that may be out of scope. Judging by the amount of stack overflow posts regarding finding Java, maybe a standalone script that just reliably finds the location of your Java SDK/JRE would be already quite the revolution :D