Add explanatory note for `<version>`
Add explanatory note for `<version>`

Per https://github.com/creationix/nvm/pull/797#discussion_r36379740

greyhwndz/nvm,domenicosolazzo/nvm,Theodeus/nvm,kumaria/nvm,slariviere/nvm,bevacqua/nvm,tianzhihen/nvm,elrasguno/nvm,kmctown/nvm,owen-it/nvm,jaawerth/nvm,devedbox/nvm,cirosantilli/nvm,jbergstroem/nvm,dfackler/nvm,parasaro92/nvm,psychoss/nvm,Richardphp/nvm,woss/nvm,kumaria/nvm,gtdeng/nvm,kmctown/nvm,owen-it/nvm,youleiy/nvm,Ingelheim/nvm,PeterDaveHelloKitchen/nvm,ljharb/nvm,wahyutaufik/nvm,PeterDaveHello/nvm,williamboman/nvm,jhliberty/nvm,cnpm/nvm,pmq20/nvm,thomasf/nvm,evocateur/nvm,psychoss/nvm,Kuzirashi/nvm,egilkh/nvm,PeterDaveHelloKitchen/nvm,JanChw/nvm,williamboman/nvm,wahyutaufik/nvm,thomasf/nvm,SampleLiao/nvm,edwmurph/nvm,hanhailong/nvm,cnpm/nvm,elrasguno/nvm,jhliberty/nvm,Ingelheim/nvm,hkdobrev/nvm,bbuck/nvm,tianzhihen/nvm,mmorejon/nvm,christophercaburog/nvm,greyhwndz/nvm,ljharb/nvm,nontage24/nvm,DigitallySeamless/nvm,icyflame/nvm,slariviere/nvm,Richardphp/nvm,egilkh/nvm,bevacqua/nvm,dfackler/nvm,Theodeus/nvm,PeterDaveHello/nvm,parasaro92/nvm,evocateur/nvm,creationix/nvm,JasonChrYoung/nvm,cjac/nvm,cirosantilli/nvm,domenicosolazzo/nvm,hkdobrev/nvm,icyflame/nvm,gtdeng/nvm,christophercaburog/nvm,mmorejon/nvm,creationix/nvm,bbuck/nvm,jaawerth/nvm,edwmurph/nvm,DigitallySeamless/nvm,pmq20/nvm,nontage24/nvm,mirydz/nvm,youleiy/nvm,Kuzirashi/nvm,JasonChrYoung/nvm,cjac/nvm,tlevine/nvm,tlevine/nvm,lukechilds/nvm,jbergstroem/nvm,devedbox/nvm,lukechilds/nvm,hanhailong/nvm,SampleLiao/nvm,JanChw/nvm,mirydz/nvm,fnogatz/swivm,woss/nvm