[FAB-9890] Fix typo, :doc:configtxgen

In build_network.rst, :doc:`configtxgen` should be
:doc:`commands/configtxgen` for the doc link to work.

Change-Id: Id1262f3d1f3eff8b9510db49b222c0127b337e6c
Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>

Author: rpjday

docs/source/build_network.rst

@@ -354,7 +354,7 @@ The ``configtxgen tool`` is used to create four configuration artifacts:
   * channel ``configuration transaction``,
   * and two ``anchor peer transactions`` - one for each Peer Org.
 
-Please see :doc:`configtxgen` for a complete description of this tool's functionality.
+Please see :doc:`commands/configtxgen` for a complete description of this tool's functionality.
 
 The orderer block is the :ref:`Genesis-Block` for the ordering service, and the
 channel configuration transaction file is broadcast to the orderer at :ref:`Channel` creation