Add build instructions for C++ dataflow example

examples/c++-dataflow/README.md

@@ -3,3 +3,55 @@
 This example shows how to create dora operators and custom nodes with C++.
 
 Dora does not provide a C++ API yet, but we can create adapters for either the C or Rust API. The `operator-rust-api` and `node-rust-api` folders implement an example operator and node based on dora's Rust API, using the `cxx` crate for bridging. The `operator-c-api` and `node-c-api` show how to create operators and nodes based on dora's C API. Both approaches work, so you can choose the API that fits your application better.
+
+## Compile and Run
+
+To try it out, you can use the [`run.rs`](./run.rs) binary. It performs all required build steps and then starts the dataflow. Use the following command to run it: `cargo run --example cxx-dataflow`.
+
+For a manual build, follow these steps:
+
+- Create a `build` folder in this directory (i.e., next to the `node.c` file)
+- Build the `cxx-dataflow-example-node-rust-api` and `cxx-dataflow-example-operator-rust-api` crates:
+  ```
+  cargo build -p cxx-dataflow-example-node-rust-api --release
+  cargo build -p cxx-dataflow-example-operator-rust-api --release
+  ```
+- Compile the `dora-node-api-c` crate into a static library.
+  - Run `cargo build -p dora-node-api-c --release`
+  - The resulting staticlib is then available under `../../target/release/libdora-node-api-c.a`.
+- Compile the `node-c-api/main.cc` (e.g. using `clang++`) and link the staticlib
+  - For example, use the following command:
+    ```
+    clang++ node-c-api/main.cc <FLAGS> -std=c++14 -ldora_node_api_c -L ../../target/release --output build/node_c_api
+    ```
+  - The `<FLAGS>` depend on the operating system and the libraries that the C node uses. The following flags are required for each OS:
+    - Linux: `-lm -lrt -ldl -pthread`
+    - macOS: `-framework CoreServices -framework Security -l System -l resolv -l pthread -l c -l m`
+    - Windows:
+      ```
+      -ladvapi32 -luserenv -lkernel32 -lws2_32 -lbcrypt -lncrypt -lschannel -lntdll -liphlpapi
+      -lcfgmgr32 -lcredui -lcrypt32 -lcryptnet -lfwpuclnt -lgdi32 -lmsimg32 -lmswsock -lole32
+      -lopengl32 -lsecur32 -lshell32 -lsynchronization -luser32 -lwinspool
+      -Wl,-nodefaultlib:libcmt -D_DLL -lmsvcrt
+      ```
+      Also: On Windows, the output file should have an `.exe` extension: `--output build/c_node.exe`
+- Compile the `operator-c-api/operator.cc` file into a shared library.
+  - For example, use the following commands:
+    ```
+    clang++ -c operator-c-api/operator.cc -std=c++14 -o build/operator_c_api.o -fPIC
+    clang++ -shared build/operator_c_api.o -o build/liboperator_c_api.so
+    ```
+    Omit the `-fPIC` argument on Windows. Replace the `liboperator_c_api.so` name with the shared library standard library prefix/extensions used on your OS, e.g. `.dll` on Windows.
+
+**Build the dora coordinator and runtime:**
+
+- Build the `dora-coordinator` executable using `cargo build -p dora-coordinator --release`
+- Build the `dora-runtime` executable using `cargo build -p dora-runtime --release`
+
+**Run the dataflow:**
+
+- Start the `dora-coordinator`, passing the paths to the dataflow file and the `dora-runtime` as arguments:
+
+  ```
+  ../../target/release/dora-coordinator run dataflow.yml ../../target/release/dora-runtime
+  ```