Updated README.md readability -- missed two lines
Updated README.md readability -- missed two lines

Missed two lines from my original pull request (https://github.com/philc/vimium/pull/1481). Basically:
Changed references to vimiim commands that were either in single-quotes or not otherwise distinguished easily to the reader as a command to be wrapped around backtick quotes so they will stand out. Here is a list of all changes made:

Line 215, 'b' updated to `b`
Line 240, 'g0' updated to `g0` and 'g$' updated to `g$`
elderbas/vimium,csmalin/vimium,Aleroniponi/vimium,douglas-larocca/vimium,willsALMANJ/vimium,Robinson10240/vimium,PickRelated/vimium,willsALMANJ/vimium,mrmr1993/vimium,Lw-Cui/vimium,justalittlenoob/vimium,PrestanceDesign/vimium,PrestanceDesign/vimium,tuchangwei/vimium,zhangmin510/vimium,wildeyes/vimium,dimatter/vimium,VPashkov/vimium,elderbas/vimium,decaffeinate-examples/vimium,zhangmin510/vimium,VPashkov/vimium,Aleroniponi/vimium,philc/vimium,willsALMANJ/vimium,justalittlenoob/vimium,Aleroniponi/vimium,elderbas/vimium,decaffeinate-examples/vimium,bkudria/vimium,justalittlenoob/vimium,PickRelated/vimium,Lw-Cui/vimium,poacher2k/vimium,douglas-larocca/vimium,hhsue/vimium,cyrixhero/vimium,dimatter/vimium,smblott-github/vimium,Lw-Cui/vimium,borgified/vimium,PrestanceDesign/vimium,hhsue/vimium,bkudria/vimium,poacher2k/vimium,zhangmin510/vimium,tuchangwei/vimium,VPashkov/vimium,bkudria/vimium,csmalin/vimium,dimatter/vimium,elegantwww/vimium,borgified/vimium,elegantwww/vimium,cyrixhero/vimium,elegantwww/vimium,PickRelated/vimium,philc/vimium,wildeyes/vimium,douglas-larocca/vimium,wildeyes/vimium,mrmr1993/vimium,hhsue/vimium,gdh1995/vimium,smblott-github/vimium,Robinson10240/vimium,Robinson10240/vimium,csmalin/vimium,philc/vimium,smblott-github/vimium,gdh1995/vimium,tuchangwei/vimium,mrmr1993/vimium,gdh1995/vimium,decaffeinate-examples/vimium,borgified/vimium,poacher2k/vimium,cyrixhero/vimium