On bootup? Are you sure? Or just when you logon. Different answers for each so you might want to expand on your need. Generally, for bootup, you create an init.d script or run it from /etc/rc.local. For login, there is a gui startup app where you can put the Mycroft script so it starts every time you login.
To find the Startup application, Select "Show Applications" then in search box, you put "Startup". It should have a "rocket" icon. Select the application, then use the "Add" button to fill in the fields. When you logon, that application runs. It can be a program or an executable script.
For scripts or programs you want to run as root at bootup, create /etc/rc.local as root (or edit it if it exists). Then add your program or script. Remember to redirect output and error to a file and/or run it with "nohup" in background so it doesn't hang your system if there is an issue. Note, best to use full pathnames for all objects. Scripts should be in "root-protected" directories like /root and not be even readable by users. Commands in scripts should have full path names for security. Using nohup insures that when the rc.local script finishes, the program or script is not terminated.
Ex:
nohup /root/myscript >/root.myscript.out 2>&1 & # so program has its own error file
nohup /bin/ps -ef & # Output goes to nohup.out.