What does "bikeshed alert" mean?

To put this into a context, someone was making a comment about some work that I've done, and she started it with "Bikeshed alert, ... (rest of the comment)". What exactly does "bikeshed alert" mean?

The remark is a play on "spoiler alert," whereby the reader is warned further reading might give away an ending. The meaning of "bike shed" can be found by searching for that term and Cyril Nothcote Parkinson. Parkinson wrote an essay comparing the amount of time a government committee would spend considering the construction of a bicycle shed and a nuclear reactor. Your writer was warning you that he or she was about to spend far too much time on a particular topic than, in reality, it might have deserved, much as I have done here.