Unable to create .make file

If drush make-generate fails with this error:

Unable to create .make file

the solution is to supply a full path to the makefile in a writeable directory:

drush make-generate /path/to/example.make

This solution might seem obvious to anyone familiar with permissions, but:

• The default error message does not give information such as "permission denied"
• Nor does it specify the directory where drush is attempting to write the file
• Many shell commands will automatically create a file in your current directory
• Finally, at least on my system, you cannot use a relative path. ./example.make won't work.

The easiest solution is probably documentation: a more informative error message, and a note about the option to use a full path in "drush --help make-generate"