Update adding-new-code-to-nest.md

adding-new-code-to-nest.md

@@ -1,6 +1,6 @@
 Adding New Code to NEST
 =======================
-This document assumes that the reader already knows [how to build NEST from source(tips-on-nest.md)].
+This document assumes that the reader already knows [how to build NEST from source](tips-on-nest.md).
 
 * If you want to add a new library inside NEST, createa a new directory inside ```nest/nest-2.6.0```. In my case, I created the directory ```nest/nest-2.6.0/nestgpu``` and wanted my new code to be inside the new library ```libnestgpu```. Inside this directory, you add your new source/header files.
 * However, your code is still not part of the NEST build system. To have your code be built with NEST, you need to do few more things.