Mention register_assert_rewrite explicitly
Mention register_assert_rewrite explicitly

It helps mentioning this explicitly in the changelog.
Fixes #1871.

MichaelAquilina/pytest,The-Compiler/pytest,hpk42/pytest,flub/pytest,nicoddemus/pytest,tomviner/pytest,jaraco/pytest,alfredodeza/pytest,tomviner/pytest,davidszotten/pytest,The-Compiler/pytest,rmfitzpatrick/pytest,txomon/pytest,eli-b/pytest,skylarjhdownes/pytest,hpk42/pytest,ddboline/pytest,pytest-dev/pytest,malinoff/pytest,RonnyPfannschmidt/pytest,nicoddemus/pytest,vmalloc/dessert,tareqalayan/pytest,markshao/pytest,Akasurde/pytest,tgoodlet/pytest,etataurov/pytest,hackebrot/pytest,pfctdayelise/pytest