Log Message:
Update gnucash-docs to 2.6.11:

More German Translation work from Mechtilde Stehmann.
New German illustrations from Mechtilde Stehmann.
Use letter size paper only in US or C locales. The rest of the
world uses metric A4 paper. The locale detection is done at configure.
Clarify that creating a postponed SX will use the original date.
Bug 759859 - Reconcilation does not convert transactions' currency
to the main one making reconcilation impossible.
Bug 760016 - 2.6.10 and master dump script error while running configure.
Bug 760407 - Note account separator isn't always a colon.