Add description in README.md

README.md

@@ -1 +1,9 @@
-# Gomu
+# Gomu
+
+Gomu is an interpreter program for mathematics written entirely in C++.
+New cool stuff can be added using modules.
+
+For the moment, available modules are:
+
+-- base (for basic mathematics)
+-- garside (for computation on braid groups)