Minor changes to the Function section in the docs

Author: Thoemi09

doc/examples/fun1.cpp

@@ -1,7 +1,4 @@
 #include <c2py/c2py.hpp>
 
-struct A {
-  int i = 3;
-  double x;
-  std::string s;
-};
+int f(int x) { return -x;}
+int f(int x, int y) { return x + y;}

doc/reference/fnt_basic.rst

@@ -88,5 +88,5 @@ or
 Template functions
 ------------------
 
-The instantiation of generic functions in discussed in :ref:`customize`.
+The instantiation of generic functions in discussed in :ref:`function_templates`.