README: Update to match changes from 2106ebf1
README: Update to match changes from 2106ebf1

This commit is the result of running `make doc`, which keeps README.rst
in sync with the reality of the default values in stbt.conf.

stb-tester/stb-tester,martynjarvis/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester,LewisHaley/stb-tester,LewisHaley/stb-tester,wmanley/stb-tester,martynjarvis/stb-tester,wmanley/stb-tester,martynjarvis/stb-tester,wmanley/stb-tester,LewisHaley/stb-tester,martynjarvis/stb-tester,wmanley/stb-tester,wmanley/stb-tester,LewisHaley/stb-tester,martynjarvis/stb-tester,LewisHaley/stb-tester,LewisHaley/stb-tester,stb-tester/stb-tester,martynjarvis/stb-tester,LewisHaley/stb-tester,martynjarvis/stb-tester