Create new files with the names below in a folder that is on your PATH. The sample command below uses the default editor to open such in your default editor. Likely TextEdit.
$ open -e /usr/local/bin/git-mrm /usr/local/bin/git-ddev
Paste the contents respectively.
Make the newly created files executable
$ chmod +x /usr/local/bin/git-mrm /usr/local/bin/git-ddev
Like every custom git command
$ git-ddev
$ git ddev
$ git-mrm
$ git mrm