Every time I start my terminal, I get ".zshrc:source:18: no such file or directory: /sourceme.sh"?
I was able to solve this issue with the following steps:
Open .zshrc and edit it. This can be done with the following:
sudo nano ~/.zshrc

From here, you may find a file, whatever it may be named (in this case, it was sourceme.sh). Delete the line that was installed in there. There are many reasons it's in there using nano. Then, save.
Where sourceme.sh came from: I downloaded another program that automatically wrote that line in when I configured it, and when I deleted, it could no longer find that file. It could be any other shell script (.sh).