Newcomers_Guide.rst: Specify the assign command
Newcomers_Guide.rst: Specify the assign command

Added a short paragraph to Step 3 of the Newcomers_Guide in which it
is clearly specified what a newcomer should do in order to get an
issue. It was a needed change so that newcomers wouldn`t work
unasigned and also it would be pretty easy for them to find the way
to assign themselves to the respective issue.

Closes https://github.com/coala/coala/issues/3495

coala/coala,coala/coala,sagark123/coala,sagark123/coala,meetmangukiya/coala,arush0311/coala,jayvdb/coala,RJ722/coala,SanketDG/coala,MariosPanag/coala,damngamerz/coala,yashLadha/coala,damngamerz/coala,coala-analyzer/coala,nemaniarjun/coala,arjunsinghy96/coala,Nosferatul/coala,MariosPanag/coala,shreyans800755/coala,refeed/coala,Balaji2198/coala,arush0311/coala,Balaji2198/coala,shreyans800755/coala,arjunsinghy96/coala,karansingh1559/coala,impmihai/coala,Asnelchristian/coala,rimacone/testing2,jayvdb/coala,CruiseDevice/coala,arjunsinghy96/coala,shreyans800755/coala,kartikeys98/coala,ayushin78/coala,NiklasMM/coala,incorrectusername/coala,kartikeys98/coala,SanketDG/coala,ayushin78/coala,refeed/coala,yashtrivedi96/coala,SanketDG/coala,jayvdb/coala,CruiseDevice/coala,meetmangukiya/coala,NiklasMM/coala,aptrishu/coala,Nosferatul/coala,Asnelchristian/coala,netman92/coala,yashLadha/coala,nemaniarjun/coala,RJ722/coala,Shade5/coala,coala-analyzer/coala,Asalle/coala,JohnS-01/coala,netman92/coala,Asnelchristian/coala,incorrectusername/coala,Shade5/coala,arush0311/coala,yashLadha/coala,rimacone/testing2,Shade5/coala,kartikeys98/coala,karansingh1559/coala,impmihai/coala,karansingh1559/coala,aptrishu/coala,incorrectusername/coala,JohnS-01/coala,sagark123/coala,nemaniarjun/coala,coala/coala,yashtrivedi96/coala,refeed/coala,Asalle/coala,CruiseDevice/coala,coala-analyzer/coala,Balaji2198/coala,damngamerz/coala,NiklasMM/coala,MariosPanag/coala,yashtrivedi96/coala,JohnS-01/coala,rimacone/testing2,aptrishu/coala,RJ722/coala,netman92/coala,impmihai/coala,ayushin78/coala,Asalle/coala,Nosferatul/coala,meetmangukiya/coala