Update readme

Author: phipsgabler

README.md

@@ -5,7 +5,18 @@
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-A new light-weight package to factor out interfaces and associated APIs for probabilistic
-programming languages (especially their modelleing languages).  The overall goals are creating an
-abstract type and minimal set of functions that will be supported all model and trace types.  Some
-other commonly used code, such as variable names, can also go here.
+A new light-weight package to factor out interfaces and associated APIs for modelling languages for
+probabilistic programming.  High level goals are:
+
+- Definition of an interface of few abstract types and a small set of functions that will be
+supported all model and trace types.
+- Provision of some commonly used functionality and data structures, e.g., for managing variable names and
+  traces.
+  
+This should facilitate reuse of functions in modelling languages, to allow end users to handle
+models in a consistent way, and to simplify interaction between different languages and sampler
+implementations, from very rich, dynamic languages like Turing.jl to highly constrained or
+simplified models such as GPs, GLMs, or plain log-density problems.
+
+A more short term goal is to start a process of cleanly refactoring and justifying parts of
+AbstractPPL.jl’s design, and hopefully to get on closer terms with Soss.jl.