Add header message to _config.yml
Add header message to _config.yml

The first thing new users to Jekyll do is open _config.yml, so this
change adds a simple welcome message to the top of it. Additionally,
it informs the user that the file is not automatically reloaded when
changed, which is a point of confusion for new users.

Related issue: https://github.com/jekyll/jekyll/issues/2302

nasht00/jekyll,xcatliu/jekyllcn,xcatliu/jekyllcn,jekyll/jekyll,zsyed91/jekyll,Kinghack/kinghack.github.com,LeuisKen/jekyllcn,alfredxing/jekyll,hartmel/jekyll,Teino1978-Corp/jekyll,ryanshaw/jekyll,alex-kovac/jekyll,zsyed91/jekyll,Teino1978-Corp/Teino1978-Corp-jekyll,bsmr-ruby/jekyll,tomjohnson1492/jekyll,dansef/jekyll,rebornix/jekyll,PepSalehi/jekyll,stomar/jekyll,nasht00/jekyll,tillgrallert/jekyll,pmarsceill/jekyll,tillgrallert/jekyll,MauroMrod/jekyll,codeclimate-testing/jekyll,Teino1978-Corp/Teino1978-Corp-jekyll,xcatliu/jekyllcn,PepSalehi/jekyll,superve/jekyll,ajhit406/jekyll,MauroMrod/jekyll,gencer/jekyll,yihangho/jekyll,hartmel/jekyll,pmarsceill/jekyll,rebornix/jekyll,codeclimate-testing/jekyll,hartmel/jekyll,superve/jekyll,gaosboy/jekyll,derekgottlieb/jekyll,FlyingWHR/jekyll,ryanshaw/jekyll,larryfox/jekyll,chrisfinazzo/jekyll,yihangho/jekyll,princeofdarkness76/jekyll,princeofdarkness76/jekyll,brint/jekyll,likong/jekyll,gaosboy/jekyll,jeffkole/jekyll,tillgrallert/jekyll,rlugojr/jekyll,larryfox/jekyll,zsyed91/jekyll,derekgottlieb/jekyll,nickg33/jekyll,Kinghack/kinghack.github.com,jekyll/jekyll,dansef/jekyll,aarvay/jekyll,jekyll/jekyll,tillgrallert/jekyll,rlugojr/jekyll,ducktyper/jekyll,FlyingWHR/jekyll,derekgottlieb/jekyll,jmepg/jekyll,mrb/jekyll,tomjohnson1492/jekyll,alfredxing/jekyll,floydpraveen/jekyll,jeffkole/jekyll,fulldecent/jekyll,darwin/jekyll,darwin/jekyll,likong/jekyll,floydpraveen/jekyll,jmepg/jekyll,Kinghack/kinghack.github.com,xiebinhqy/jklly_china,alfredxing/jekyll,brint/jekyll,fulldecent/jekyll,ZDroid/jekyll,alex-kovac/jekyll,jaybe-jekyll/jekyll,getandpost/jekyll.github.io,tomjohnson1492/jekyll,Teino1978-Corp/jekyll,tillgrallert/jekyll,getandpost/jekyll.github.io,howkj1/jekyll,FlyingWHR/jekyll,chrisfinazzo/jekyll,bsmr-ruby/jekyll,x-way/jekyll,jaybe-jekyll/jekyll,floydpraveen/jekyll,nickg33/jekyll,jekyll/jekyll,mrb/jekyll,nasht00/jekyll,xiebinhqy/jklly_china,howkj1/jekyll,tomjohnson1492/jekyll,gencer/jekyll,jeffkole/jekyll,rasa2011/rasa2011.github.io,xiebinhqy/jklly_china,noikiy/jekyll,derekgottlieb/jekyll,nickg33/jekyll,rasa2011/rasa2011.github.io,xiebinhqy/jklly_china,princeofdarkness76/jekyll,fulldecent/jekyll,stomar/jekyll,x-way/jekyll,pmarsceill/jekyll,superve/jekyll,aarvay/jekyll,larryfox/jekyll,jeffkole/jekyll,nasht00/jekyll,Strangehill/jekyll,ZDroid/jekyll,noikiy/jekyll,rlugojr/jekyll,pmarsceill/jekyll,Strangehill/jekyll,Strangehill/jekyll,ryanshaw/jekyll,jmepg/jekyll,alex-kovac/jekyll,jaybe-jekyll/jekyll,thetaxman/jekyll,gencer/jekyll,Strangehill/jekyll,gencer/jekyll,ajhit406/jekyll,LeuisKen/jekyllcn,xcatliu/jekyllcn,alfredxing/jekyll,codeclimate-testing/jekyll,Teino1978-Corp/Teino1978-Corp-jekyll,rlugojr/jekyll,thetaxman/jekyll,darwin/jekyll,noikiy/jekyll,howkj1/jekyll,chrisfinazzo/jekyll,gaosboy/jekyll,zsyed91/jekyll,MauroMrod/jekyll,bsmr-ruby/jekyll,mrb/jekyll,noikiy/jekyll,stomar/jekyll,ducktyper/jekyll,alex-kovac/jekyll,bsmr-ruby/jekyll,princeofdarkness76/jekyll,yhironaka/yhironaka.github.io,dansef/jekyll,alex-kovac/jekyll,ajhit406/jekyll,ZDroid/jekyll,thetaxman/jekyll,PepSalehi/jekyll,ducktyper/jekyll,darwin/jekyll,gencer/jekyll,mrb/jekyll,brint/jekyll,rebornix/jekyll,yihangho/jekyll,ajhit406/jekyll,likong/jekyll,ryanshaw/jekyll,tomjohnson1492/jekyll,chrisfinazzo/jekyll,x-way/jekyll,LeuisKen/jekyllcn,getandpost/jekyll.github.io,jaybe-jekyll/jekyll,stomar/jekyll,Teino1978-Corp/jekyll,x-way/jekyll,fulldecent/jekyll,rasa2011/rasa2011.github.io,floydpraveen/jekyll,aarvay/jekyll,brint/jekyll,Strangehill/jekyll