coala_main.py: Add param doc for 'arg_parser'
coala_main.py: Add param doc for 'arg_parser'

Closes https://github.com/coala/coala/issues/3016

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