traits.md: Fix example of using traits to match description
traits.md: Fix example of using traits to match description

traits.md said:

If we add a `use` line right above `main` and make the right things public,
everything is fine:

However, the use line was actually placed at the top of the file instead.  Move
the use line to right above main.  That also makes the example more evocative
of cases where the module is defined in a separate file.
vhbit/rust,dwillmer/rust,l0kod/rust,krzysz00/rust,krzysz00/rust,pshc/rust,jashank/rust,andars/rust,graydon/rust,mvdnes/rust,kwantam/rust,mihneadb/rust,jroesch/rust,mdinger/rust,aepsil0n/rust,aepsil0n/rust,philyoon/rust,aneeshusa/rust,victorvde/rust,seanrivera/rust,zubron/rust,XMPPwocky/rust,GBGamer/rust,dwillmer/rust,jroesch/rust,XMPPwocky/rust,victorvde/rust,omasanori/rust,miniupnp/rust,mvdnes/rust,mihneadb/rust,mvdnes/rust,sae-bom/rust,aneeshusa/rust,aepsil0n/rust,philyoon/rust,TheNeikos/rust,ejjeong/rust,rohitjoshi/rust,graydon/rust,nwin/rust,seanrivera/rust,mdinger/rust,mihneadb/rust,omasanori/rust,cllns/rust,reem/rust,ejjeong/rust,l0kod/rust,philyoon/rust,victorvde/rust,graydon/rust,zubron/rust,pshc/rust,aneeshusa/rust,miniupnp/rust,vhbit/rust,aepsil0n/rust,aneeshusa/rust,nwin/rust,pshc/rust,pelmers/rust,nwin/rust,mihneadb/rust,KokaKiwi/rust,cllns/rust,mihneadb/rust,gifnksm/rust,miniupnp/rust,aidancully/rust,gifnksm/rust,rohitjoshi/rust,aidancully/rust,omasanori/rust,zachwick/rust,jashank/rust,pshc/rust,ruud-v-a/rust,aidancully/rust,vhbit/rust,miniupnp/rust,rohitjoshi/rust,avdi/rust,vhbit/rust,philyoon/rust,nwin/rust,mdinger/rust,pshc/rust,jashank/rust,mdinger/rust,graydon/rust,jroesch/rust,ruud-v-a/rust,nwin/rust,mdinger/rust,sae-bom/rust,nwin/rust,rohitjoshi/rust,KokaKiwi/rust,victorvde/rust,jashank/rust,XMPPwocky/rust,dwillmer/rust,zubron/rust,vhbit/rust,gifnksm/rust,omasanori/rust,reem/rust,nwin/rust,zubron/rust,l0kod/rust,robertg/rust,krzysz00/rust,ejjeong/rust,TheNeikos/rust,avdi/rust,cllns/rust,victorvde/rust,ejjeong/rust,kwantam/rust,andars/rust,zubron/rust,TheNeikos/rust,graydon/rust,GBGamer/rust,pshc/rust,avdi/rust,avdi/rust,reem/rust,KokaKiwi/rust,jashank/rust,pelmers/rust,seanrivera/rust,dwillmer/rust,ruud-v-a/rust,avdi/rust,GBGamer/rust,XMPPwocky/rust,reem/rust,miniupnp/rust,KokaKiwi/rust,rohitjoshi/rust,seanrivera/rust,victorvde/rust,aidancully/rust,jashank/rust,XMPPwocky/rust,reem/rust,pelmers/rust,rohitjoshi/rust,gifnksm/rust,carols10cents/rust,mvdnes/rust,krzysz00/rust,GBGamer/rust,miniupnp/rust,dwillmer/rust,seanrivera/rust,cllns/rust,gifnksm/rust,zachwick/rust,aneeshusa/rust,TheNeikos/rust,sae-bom/rust,l0kod/rust,aepsil0n/rust,ruud-v-a/rust,zubron/rust,jashank/rust,miniupnp/rust,l0kod/rust,vhbit/rust,sae-bom/rust,philyoon/rust,zachwick/rust,GBGamer/rust,l0kod/rust,carols10cents/rust,vhbit/rust,l0kod/rust,omasanori/rust,carols10cents/rust,graydon/rust,ruud-v-a/rust,reem/rust,dwillmer/rust,KokaKiwi/rust,KokaKiwi/rust,robertg/rust,mvdnes/rust,carols10cents/rust,zachwick/rust,GBGamer/rust,kwantam/rust,jroesch/rust,kwantam/rust,cllns/rust,l0kod/rust,aneeshusa/rust,pshc/rust,miniupnp/rust,gifnksm/rust,GBGamer/rust,pelmers/rust,pshc/rust,jroesch/rust,mihneadb/rust,kwantam/rust,omasanori/rust,sae-bom/rust,mvdnes/rust,robertg/rust,TheNeikos/rust,GBGamer/rust,robertg/rust,pelmers/rust,ejjeong/rust,krzysz00/rust,robertg/rust,andars/rust,XMPPwocky/rust,dwillmer/rust,jroesch/rust,ruud-v-a/rust,cllns/rust,ejjeong/rust,avdi/rust,aepsil0n/rust,aidancully/rust,kwantam/rust,jroesch/rust,pelmers/rust,jashank/rust,philyoon/rust,carols10cents/rust,krzysz00/rust,aidancully/rust,seanrivera/rust,TheNeikos/rust,dwillmer/rust,carols10cents/rust,vhbit/rust,zubron/rust,zubron/rust,mdinger/rust,zachwick/rust,sae-bom/rust,robertg/rust,andars/rust,nwin/rust,jroesch/rust,andars/rust,andars/rust,zachwick/rust