Proposal floats -doctool flag for go doc -http

A new proposal would add a -doctool flag to go doc, letting the local HTML server run against alternative pkgsite versions instead of the hardcoded one. Small surface, but anyone who has watched go doc -http drift behind pkgsite will recognise the itch. On the writing side, one developer walks through building a tiny in-memory database in Go to figure out what Redis actually does beyond "hash table", and another reports a 61% parser CPU drop after replacing encoding/json with a hand-written unmarshaller. Both are the kind of post that earns its benchmark.