doc: start go 1.2 notes

This is a file of hints, not a file of polished text.
Let's not try to do polished text until we start the
release process.

R=golang-dev, gri
CC=golang-dev
https://golang.org/cl/9750043

doc/go1.2.txt

+This file collects notes about what has changed since Go 1.1
+and should be mentioned in the Go 1.2 release notes.
+During the Go 1.2 release process it will be necessary to convert
+it to HTML, similar to go1.1.html, but for now it is a text file,
+to make the process of keeping it up-to-date more lightweight.
+
+Please keep the descriptions to a single line, starting with the
+package or cmd/xxx directory name, and ending in a CL number.
+Please keep the list sorted (as in sort.Strings of the lines).
+
+io: Copy prioritizes WriterTo over ReaderFrom (CL 9462044).