SDK: Improve the C++ SDK readme, and add some missing docstrings.

R=vardhan@google.com

Review URL: https://codereview.chromium.org/1760403003 .

sdk_build/data/common/download_file_from_google_storage.py

diff --git a/sdk_build/data/common/download_file_from_google_storage.py b/sdk_build/data/common/download_file_from_google_storage.py
index 28feb4d..2798883 100755
--- a/sdk_build/data/common/download_file_from_google_storage.py
+++ b/sdk_build/data/common/download_file_from_google_storage.py
@@ -3,7 +3,8 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-#FIXME
+"""Script for downloading a file from Google Cloud Storage."""
+
 
 import argparse
 import hashlib
@@ -18,7 +19,9 @@
 
 
 def _DownloadFile(source):
-  """FIXME"""
+  """Downloads |source| from Google Cloud Storage. |source| should be a path,
+  including the bucket name (e.g., if the full URL is gs://mojo/a/b/c.xyz,
+  |source| should be "mojo/a/b/c.xyz")."""
 
   try:
     conn = httplib.HTTPSConnection("storage.googleapis.com")
@@ -40,7 +43,7 @@
                       help="SHA-1 hash for the downloaded file")
   parser.add_argument("--executable", action="store_true",
                       help="make the downloaded file executable")
-  parser.add_argument("source", help="source path, including bucket name")
+  parser.add_argument("source", help="source path, including the bucket name")
   parser.add_argument("destination", help="destination path")
   args = parser.parse_args()
 

sdk_build/data/cpp/README-sdk.md

diff --git a/sdk_build/data/cpp/README-sdk.md b/sdk_build/data/cpp/README-sdk.md
index be620c7..6144fa8 100644
--- a/sdk_build/data/cpp/README-sdk.md
+++ b/sdk_build/data/cpp/README-sdk.md
@@ -25,18 +25,19 @@
 
 ## Set up
 
-To generate code from Mojom files, one needs the Mojom tool. Running the
-following causes the binary to be downloaded:
+To get started quickly, just run the following:
+
+    $ mojo_sdk_setup/setup.sh
+
+This is equivalent to performing the steps below separately:
 
     $ mojo_sdk_setup/download_mojom_tool.sh
-
-The included Makefile uses clang. The following downloads a suitable version of
-clang:
-
     $ mojo_sdk_setup/download_clang.sh
 
-(One should be able to build using another compiler with sufficient C++11
-support.)
+The first downloads a binary for the Mojom tool, which is needed to generate
+code from Mojom files. The second downloads a suitable version of clang, which
+is needed by the included Makefile. (One should also be able to build using
+another compiler with sufficient C++11 support.)
 
 ## Building the examples