README-developers.md: Added pull request checklist.
README-developers.md: Added pull request checklist.

BrutalCode/NLog,MoaidHathot/NLog,bjornbouetsmith/NLog,AndreGleichner/NLog,snakefoot/NLog,UgurAldanmaz/NLog,tetrodoxin/NLog,NLog/NLog,littlesmilelove/NLog,nazim9214/NLog,tetrodoxin/NLog,bjornbouetsmith/NLog,luigiberrettini/NLog,hubo0831/NLog,michaeljbaird/NLog,michaeljbaird/NLog,nazim9214/NLog,bhaeussermann/NLog,hubo0831/NLog,bryjamus/NLog,luigiberrettini/NLog,bhaeussermann/NLog,breyed/NLog,sean-gilliam/NLog,ie-zero/NLog,kevindaub/NLog,breyed/NLog,MoaidHathot/NLog,ilya-g/NLog,304NotModified/NLog,kevindaub/NLog,ilya-g/NLog,BrutalCode/NLog,tohosnet/NLog,tohosnet/NLog,MartinTherriault/NLog,bryjamus/NLog,UgurAldanmaz/NLog,MartinTherriault/NLog,littlesmilelove/NLog,ie-zero/NLog,AndreGleichner/NLog