[FAB-4494] Add missing step in Getting Started doc

This adds instruction to change to the proper subdirectory before
running network_setup.sh.

Change-Id: Ibe84ae56ef7731063305b20752a23068098bcab6
Signed-off-by: Arnaud J Le Hors <lehors@us.ibm.com>

docs/source/getting_started.rst

@@ -76,6 +76,10 @@ script will use a default name of ``mychannel``.  The cli timeout parameter
 is an optional value; if you choose not to set it, then your cli container
 will exit upon conclusion of the script.
 
+Change to the release subdirectory corresponding to your architecture
+that was created in the first step, such as ``release/windows-amd64``,
+then execute one of the following commands:
+
 .. code:: bash
 
               ./network_setup.sh up