Make sure PATH is correctly set on Linux after cs setup

Coursier sets the PATH by editing .profile/.bash_profile/.zprofile, but
while these files get sourced on startup by the default Terminal app on
macOS, other terminals don't behave that way, especially on Linux where
they usually are only sourced when logging in.

labs/tools-setup.md

@@ -32,6 +32,8 @@ chmod +x cs
 ./cs setup -y --jvm 8 --apps cs,sbt
 ```
 
+Please reboot after this point.
+
 ### On macOS
 
 First, install the Homebrew package manager: