add release notes for 1.2 (#8933)
add release notes for 1.2 (#8933)

* add release notes for 1.2

* typo

* quality

ericmjl/bokeh,ericmjl/bokeh,timsnyder/bokeh,timsnyder/bokeh,bokeh/bokeh,bokeh/bokeh,bokeh/bokeh,bokeh/bokeh,ericmjl/bokeh,timsnyder/bokeh,bokeh/bokeh,ericmjl/bokeh,timsnyder/bokeh,timsnyder/bokeh,ericmjl/bokeh