on windows 10 using the 64bit insiders edition the command should be:
git config --global core.editor "'C:\Program Files\Microsoft VS Code Insiders\bin\code-insiders.cmd'"
you can also rename the 'code-insiders.cmd' to 'code.cmd' in the 'Program Files' directory, in this way you can now use the command 'code .' to start editing the files on the . directory
