C++ SDK: Add a README.md.
Also update sdk_build/data/README.md.
R=vardhan@google.com
Review URL: https://codereview.chromium.org/1764303002 .
diff --git a/sdk_build/README.md b/sdk_build/README.md
index f8cc65a..4cd0a5e 100644
--- a/sdk_build/README.md
+++ b/sdk_build/README.md
@@ -2,3 +2,19 @@
This directory contains (or will contain) tools, scripts, and data for building
SDKs (for various languages and platforms).
+
+## build_sdk.py
+
+This is a script that creates a directory containing an "SDK" using the
+instructions in a given "SDK specification file" and data from the current git
+repository (which should be clean; for testing purposes, you may give the
+`--allow-dirty-tree` flag).
+
+For example:
+
+ $ ./build_sdk.py data/cpp/cpp.sdk /tmp/my_cpp_sdk
+
+This creates an SDK for C++ in `/tmp/my_cpp_sdk`.
+
+This script does not handle packaging such an SDK (e.g., into a tarball) or
+uploading it (e.g., to Google Cloud Storage).
diff --git a/sdk_build/data/cpp/README-sdk.md b/sdk_build/data/cpp/README-sdk.md
new file mode 100644
index 0000000..be620c7
--- /dev/null
+++ b/sdk_build/data/cpp/README-sdk.md
@@ -0,0 +1,53 @@
+# Mojo C++ SDK
+
+This is a minimal SDK for writing/building Mojo applications/services in C++.
+Currently, it supports building for Linux. (**TODO(vtl)**: Support other
+configurations/targets.)
+
+It includes a simple Makefile that demonstrates building a couple of simple
+example applications/services (in `examples/hello_mojo`). Note that the Makefile
+is intended to be illustrative, and not for maximal correctness or practicality
+(for example, it does not deal with dependencies correctly).
+
+Users of the SDK are expected to set up builds in an appropriate way for their
+situation, but the Makefile should show the key steps (in particular, generating
+the C++ source files from Mojom files).
+
+## Prerequisites
+
+To fetch the Mojom tool and clang:
+* bash
+* python 2.7
+
+To build the examples:
+* binutils
+* make
+
+## Set up
+
+To generate code from Mojom files, one needs the Mojom tool. Running the
+following causes the binary to be downloaded:
+
+ $ 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.)
+
+## Building the examples
+
+To build the included examples:
+
+ $ make -j8
+
+(or similar). All the build output is put into the `out` subdirectory. The
+examples themselves are `hello_mojo_client.mojo` and `hello_mojo_server.mojo`.
+
+## See also
+
+* [The Mojo project on GitHub](https://github.com/domokit/mojo)
+* [Mojo documentation](https://github.com/domokit/mojo/tree/master/docs)
diff --git a/sdk_build/data/cpp/cpp.sdk b/sdk_build/data/cpp/cpp.sdk
index f99e212..d96cd08 100644
--- a/sdk_build/data/cpp/cpp.sdk
+++ b/sdk_build/data/cpp/cpp.sdk
@@ -93,3 +93,6 @@
# Bring in the license and authors files.
CopyFiles(["LICENSE", "AUTHORS"], "")
+
+# Put in the README.md for the SDK.
+WriteFile("README.md", ReadFile("sdk_build/data/cpp/README-sdk.md"))
