Move DEVELOPMENT.md into book.

book/src/SUMMARY.md

@@ -1,6 +1,7 @@
 # Summary
 
 [DarkFi](README.md)
+- [Development](development.md)
 - [zkas](zkas/zkas.md)
   - [Examples](zkas/examples.md)
     - [Sapling payment scheme](zkas/examples/sapling.md)