FDS docs need further clarification about FDS input file path

[alahiff]

Whenever I've followed the FDS integration documentation (i.e. https://docs.simvue.io/integrations/fds/#usage) I always first get this error:

ERROR(102): Input file example1.fds not found in the current directory.

The docs should make it clear that you should specify the full path to the FDS input file, especially if you specify a working directory that doesn't already exist.

I know this is quite simple, but we should try to increase the chances things will work the first time for new users :-)

[wk9874]

Updated to make this clearer :)