asset: warn asset.Open must not be called from init.
asset: warn asset.Open must not be called from init.

Currently there is no easy way to fix golang/go#12077
so we document it.

Fixes golang/go#12077

Change-Id: I6b37ae375673c055152dad5b93e180d9831aef76
Reviewed-on: https://go-review.googlesource.com/13430
Reviewed-by: David Crawshaw <a2f0bf29257797dd66800b4fbb9945c3e216c004@golang.org>

qskycolor/mobile,tempbottle/mobile,golang/mobile,qskycolor/mobile,xing/gomobile,xing/gomobile,goldcaddy77/mobile,lonphy23t/mobile,xing/gomobile,ichu501/mobile,cainiaocome/mobile,steeve/mobile,tempbottle/mobile,DanielWorld/mobile,lonphy23t/mobile,0x90sled/mobile,b54898533/mobile,b54898533/mobile,samanalysis/mobile,b54898533/mobile,steeve/mobile,ichu501/mobile,cainiaocome/mobile,MaxCy330/mobile,goldcaddy77/mobile,swisspol/mobile,ppamorim/mobile,samanalysis/mobile,swisspol/mobile,ichu501/mobile,b54898533/mobile,0x90sled/mobile,MaxCy330/mobile,samanalysis/mobile,freeman0211/mobile,ppamorim/mobile,tempbottle/mobile,ichu501/mobile,cainiaocome/mobile,lonphy23t/mobile,DanielWorld/mobile,DanielWorld/mobile,DanielWorld/mobile,freeman0211/mobile,b54898533/mobile,ppamorim/mobile,lonphy23t/mobile,MaxCy330/mobile,swisspol/mobile,tempbottle/mobile,golang/mobile,MaxCy330/mobile,freeman0211/mobile,cainiaocome/mobile,xing/gomobile,lonphy23t/mobile,swisspol/mobile,0x90sled/mobile,steeve/mobile,0x90sled/mobile,goldcaddy77/mobile,qskycolor/mobile,steeve/mobile,samanalysis/mobile,swisspol/mobile,0x90sled/mobile,golang/mobile,goldcaddy77/mobile,goldcaddy77/mobile,ichu501/mobile,cainiaocome/mobile,golang/mobile,tempbottle/mobile,ppamorim/mobile,ppamorim/mobile,qskycolor/mobile,samanalysis/mobile,xing/gomobile,freeman0211/mobile,MaxCy330/mobile