[MapProxy] typo's in startup documentation

[Anne Blankert]

 Hello list,

when starting to work with MapProxy, I noticed some small problems in
the documentation:

According to the documentation I should/can use the following syntaxes
for the services.yaml:

transparent: true
supported_srs: 'EPSG:4326'

Version 0.8.4 does not like that syntax, instead, it should be:

transparent: 'true'
supported_srs: ['EPSG:4326']

Anne