Use case: A new user installs the tool and wants to learn to use it. The first thing he tries is
obraz --help. Currently the program starts working in the current directory, possibly modifying and overwriting files. The user has no way to learn how to use the program, nor to understand what's happenning.
Solution: the program should not do anything when the user asks for help. It may display a short usage message and point to the online documentation if small line count matters. The message should explain that the program is expected to be run in the directory with the site source. Optional command line argument may allow for building site in another directory (useful for automation).
P.S. You may consider making the path argument obligatory, but it would break the current behaviour.