fix(tool/judgers.md): wrong usage in building lemon

fix(tool/judgers.md): wrong usage in building lemon

1.  we can pass parameter into `./make` instead of using `sed` to modify the file,
    `-jn` can be passed although `-j n` can't.
2.  we can install the executable file into PATH instead of throwing it into home dir.

the result of git blame: https://github.com/OI-wiki/OI-wiki/commit/47acc594f2d94423d319a7b1ee83546ad29552a6