I am a new user of Git. I have forked a repository called Spoon-Knife (available for practicing forking with Git). Then, I cloned it locally by running
git c
I got this error because the instruction on the Web was
git checkout https://github.com/veripool/verilog-mode
which I did in a directory where (on my own initiative) i had run git init.
The correct Web instruction (for newbies like me) should have been
git clone https://github.com/veripool/verilog-mode