Docs/guide/de: minor corrections of spelling and an extension by Martin Mainka

He wrote: ... extended the description of the base account set by a cash account(Asset:Cash), since it is uncommon in germany to pay groceries and other small commodities by check.

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash-docs/trunk@23667 57a11ea4-9604-0410-9ed3-97b8803252fd