Rearrange sources (#4997)

src/xrpld/README.md

@@ -0,0 +1,9 @@
+# Ripple Source Guidelines
+
+Each folder contains a single module following the newest style:
+
+- One class per header
+- As much implementation hidden as possible
+- All major interfaces are abstract
+- Every class is documented
+- Each module focuses on solving one problem