adding bandshift params + fixing docs + other small fix

[sgiardie]

Adding bandpass shift params defaults in Foreground.yaml + expanding the docs + fixing the example yaml file

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.24%. Comparing base (91779eb) to head (191a41e).

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #93   +/-   ##
=======================================
  Coverage   85.24%   85.24%           
=======================================
  Files           3        3           
  Lines         454      454           
=======================================
  Hits          387      387           
  Misses         67       67           

Files with missing lines	Coverage Δ
mflike/foreground.py	89.24% <ø> (ø)
mflike/mflike.py	82.75% <ø> (ø)

[xgarrido]

Fine to merge