[minor] ReadTool ignores documented negative offset

[Scratchydisk]

The offset parameter is documented as supporting negative values (read.py:24): "Negative values count backwards from the end (e.g. -1 is the last line)." But the implementation silently resets any negative offset to 1 (read.py:53-54):

if offset is None or offset < 0:
    offset = 1

So the documented count-from-end behaviour is unimplemented — offset=-1 reads from the start, not the last line.

Suggested fix: implement the from-end semantics, or remove the claim from the parameter description.