Looks like you didn't install CocoaPods.
To do that you install it through ruby gems, like this:
sudo gem install cocoapods
If you don't have admin privileges, try:
gem install cocoapods --user-install
if the 1st command doesn't work, try the 2nd command
sudo gem install cocoapodssudo gem install -n /usr/local/bin cocoapods
In my case, the 2nd command worked
For OS Catalina (as of December 2019)
gem install -n /usr/local/bin cocoapods