Document installation from binary release packages

Most Gerrit2 end users will be installing from binary releases
and not from source.  Covering that in the docs will help them
to get started faster.

The "Building from source" section was out of date, due to the
recent changes about not recursing into certain dependencies.
This section has been improved with documentation on how to get
the sources from repo, and how to ensure the dependencies are
installed properly.

Signed-off-by: Shawn O. Pearce <sop@google.com>

Documentation/install.txt

@@ -1,31 +1,45 @@
 Gerrit2 - Installation
 ======================
 
-You need Apache Maven to compile the code, and a SQL database
+You need a SQL database to house the Gerrit2 metadata.  Currently
-to house the Gerrit2 metadata.  PostgreSQL is currently the only
+PostgreSQL is the only supported database.
-supported database.
 
 Important Links
 ---------------
 
-Apache Maven:
-
-* http://maven.apache.org/download.html[Download]
-* http://maven.apache.org/run-maven/index.html[Running Maven]
-
 PostgreSQL:
 
 * http://www.postgresql.org/docs/[Documentation]
 
-Build Gerrit
+Downloading Gerrit
-------------
+------------------
 
-Build the application distribution:
+Current and past binary releases of Gerrit can be obtained from
+the downloads page at the project site:
+
+* http://code.google.com/p/gerrit/downloads/list[Gerrit Downloads]
+
+Download a `*.bin.tar.bz2` package and untar it locally with
+`tar jtf gerrit-2.0.bin.tar.bz2` (or whatever the downloaded
+file was).
+
+Building Gerrit From Source
+---------------------------
+
+Alternatively, you can build the application distribution using
+Maven from a source download obtained directly from Git:
 
 ====
+  mkdir gerrit2
+  cd gerrit2
+  repo init -u git://android.git.kernel.org/tools/manifest.git
+
+  (cd jgit/jgit-maven/jgit && mvn install)
+  (cd mina_sshd && mvn install)
+
   cd appdist
   mvn clean install
-  cd appdist/target/gerrit-*-bin.dir/gerrit-*
+  cd target/gerrit-*-bin.dir/gerrit-*
 ====
 
 The first build may take a while as dependencies are searched
@@ -33,8 +47,13 @@ for and downloaded from Maven distribution repositories.
 
 Unfortunately you need to install to your local Maven repository
 (typically under `~/.m2`) in order to fully build all of the source
-based dependencies.  Core dependencies for Gerrit are still under
+based dependencies.  Some core dependencies for Gerrit are still
-active development and have not made final releases yet.
+under active development and have not made final releases yet.
+
+Apache Maven:
+
+* http://maven.apache.org/download.html[Download]
+* http://maven.apache.org/run-maven/index.html[Running Maven]
 
 Setting up the Database
 -----------------------