BIP66: link to disclosure of consensus failure bug

BIP author: @sipa Recently, a developer learning about Bitcoin contacted me with some questions about BIP66 and I discovered through our conversation that he wasn't aware of what I believe is this important context for the soft fork. I sent him a link, but I'd like to propose linking to it directly from the BIP for the historical record. I know modifying *final* BIPs is frowned upon, so if this is unacceptable, I'll add it instead to the wiki page indicated by the Comments-URI field.

Specification