Mention Gitian building script in doc.

doc/gitian-building.md

@@ -336,6 +336,8 @@ There will be a lot of warnings printed during the build of the image. These can
 Getting and building the inputs
 --------------------------------
 
+At this point you have two options, you can either use the automated script (found in [contrib/gitian-build.sh](/contrib/gitian-build.sh)) or you could manually do everything by following this guide. If you're using the automated script, then run it with the "--setup" command. Afterwards, run it with the "--build" command (example: "contrib/gitian-building.sh -b signer 0.13.0"). Otherwise ignore this.
+
 Follow the instructions in [doc/release-process.md](release-process.md#fetch-and-create-inputs-first-time-or-when-dependency-versions-change)
 in the bitcoin repository under 'Fetch and create inputs' to install sources which require
 manual intervention. Also optionally follow the next step: 'Seed the Gitian sources cache

doc/release-process.md

@@ -17,6 +17,8 @@ Before every major release:
 
 ### First time / New builders
 
+If you're using the automated script (found in [contrib/gitian-build.sh](/contrib/gitian-build.sh)), then at this point you should run it with the "--setup" command. Otherwise ignore this.
+
 Check out the source code in the following directory hierarchy.
 
     cd /path/to/your/toplevel/build
@@ -60,6 +62,8 @@ Tag version (or release candidate) in git
 
 ### Setup and perform Gitian builds
 
+If you're using the automated script (found in [contrib/gitian-build.sh](/contrib/gitian-build.sh)), then at this point you should run it with the "--build" command. Otherwise ignore this.
+
 Setup Gitian descriptors:
 
     pushd ./bitcoin