* Update macos.md
added a useful information regarding the path where java is installed, if someone has problems to find it
* Update macos.md
again, just made clear how to get the path to the installation (spark)
I believe using `brew cask` here is incorrect (at least for me it didn't work)
1. `cask` has been deprecated since version `2.6.0` (see [changelog](https://brew.sh/2020/12/01/homebrew-2.6.0/))
2. `brew install --cask java` does not work either (no cask `java`), but `brew install java` does work