Add NetBSD build instruction links

Author: axvr

doc/README.md

@@ -42,6 +42,7 @@ The following are developer notes on how to build Bitcoin on your native platfor
 - [Unix Build Notes](build-unix.md)
 - [Windows Build Notes](build-windows.md)
 - [OpenBSD Build Notes](build-openbsd.md)
+- [NetBSD Build Notes](build-netbsd.md)
 - [Gitian Building Guide](gitian-building.md)
 
 Development

doc/build-unix.md

@@ -2,7 +2,8 @@ UNIX BUILD NOTES
 ====================
 Some notes on how to build Bitcoin Core in Unix.
 
-(for OpenBSD specific instructions, see [build-openbsd.md](build-openbsd.md))
+(For BSD specific instructions, see [build-openbsd.md](build-openbsd.md) and/or
+[build-netbsd.md](build-netbsd.md))
 
 Note
 ---------------------