Add more information to test-layout docs as discussed during PR
Add more information to test-layout docs as discussed during PR

markshao/pytest,Akasurde/pytest,tareqalayan/pytest,nicoddemus/pytest,pfctdayelise/pytest,nicoddemus/pytest,skylarjhdownes/pytest,pytest-dev/pytest,The-Compiler/pytest,rmfitzpatrick/pytest,tomviner/pytest,MichaelAquilina/pytest,jaraco/pytest,hackebrot/pytest,ddboline/pytest,alfredodeza/pytest,flub/pytest,txomon/pytest,etataurov/pytest,The-Compiler/pytest,tgoodlet/pytest,tomviner/pytest,davidszotten/pytest,RonnyPfannschmidt/pytest,vmalloc/dessert