Adapt migration documentation to gsettings introduction

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash-docs/trunk@23764 57a11ea4-9604-0410-9ed3-97b8803252fd
First documention updates for credit notes

This commit partly implements feature request 687477

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash-docs/trunk@23765 57a11ea4-9604-0410-9ed3-97b8803252fd