add opam descr

.gitignore

@@ -9,6 +9,6 @@
 *~
 *.bak
 .coq-native/
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+Makefile.coq*
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descr

+This project contains an extended "Standard Library" for Coq called coq-std++.
+The key features of this library are as follows:
+
+- It provides a great number of definitions and lemmas for common data
+  structures such as lists, finite maps, finite sets, and finite multisets.
+- It uses type classes for common notations (like `∅`, `∪`, and Haskell-style
+  monad notations) so that these can be overloaded for different data structures.
+- It uses type classes to keep track of common properties of types, like it
+  having decidable equality or being countable or finite.
+- Most data structures are represented in canonical ways so that Leibniz
+  equality can be used as much as possible (for example, for maps we have
+  `m1 = m2` iff `∀ i, m1 !! i = m2 !! i`). On top of that, the library provides
+  setoid instances for most types and operations.
+- It provides various tactics for common tasks, like an ssreflect inspired
+  `done` tactic for finishing trivial goals, a simple breadth-first solver
+  `naive_solver`, an equality simplifier `simplify_eq`, a solver `solve_proper`
+  for proving compatibility of functions with respect to relations, and a solver
+  `set_solver` for goals involving set operations.
+- It is entirely dependency- and axiom-free.