Adjust text for ExponentialFamilyProjection.jl

[bvdmitri]

This PR improves the text about ExponentialFamilyProjection and also notes RxInfer as a parent package.

Thanks @kellertuer

Ref ReactiveBayes/ExponentialFamilyProjection.jl#37

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.90%. Comparing base (ba6979e) to head (6f7d6e3).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #409   +/-   ##
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  Coverage   99.90%   99.90%           
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  Files          77       77           
  Lines        8220     8220           
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  Hits         8212     8212           
  Misses          8        8           

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[kellertuer]

Thanks that was exactly what I was asking for to make it more precise. Will merge this and it will be part of the next release then.