update index

index.md

@@ -1,5 +1,29 @@
 # Sidekick
 
-## Documentation
+Sidekick is an OCaml framework to implement and use
+[SMT solvers](https://en.wikipedia.org/wiki/Satisfiability_modulo_theories)
+based on [CDCL](https://en.wikipedia.org/wiki/Conflict-driven_clause_learning).
 
-- [dev](dev/index.html)
+It is heavily functorized (parametrized) so it can use user-provided data structures,
+term representation, etc. and each part is _potentially_ swappable, even the SAT solver.
+
+Sidekick is composed of a few libraries:
+
+- `sidekick` contains the core type definitions, a congruence closure,
+  some theories (boolean formuals, algebraic datatypes),
+  and a solver implementation based on [mSAT](https://github.com/Gbury/mSAT).
+
+  `Sidekick_core` is the most important module to read there.
+- `sidekick-arith` depends on [Zarith](https://github.com/ocaml/Zarith)
+  for arbitrary-precision computations, and provides a LRA theory based
+  on an implementation of the Simplex algorithm.
+- `sidekick-bin` is an executable that uses the previous building blocks
+  to implement a concrete SMT solver. It is useful for testing, but
+  can also be used as a normal SMT solver on the command line.
+
+  It contains examples of how to instantiate the functors of `sidekick`
+  and `sidekick-arith`.
+
+## API Documentation
+
+- [development docs](dev/index.html) (docs following the master branch)