Add embind example to Bazel docs (#910)

* Add embind example to Bazel docs

* address feedback

bazel/test_external/.gitignore

@@ -0,0 +1,4 @@
+bazel-bin
+bazel-out
+bazel-test_external
+bazel-testlogs

bazel/test_external/BUILD

@@ -10,3 +10,22 @@ wasm_cc_binary(
     cc_target = ":hello-world",
 )
 
+cc_binary(
+    name = "hello-embind",
+    srcs = ["hello-embind.cc"],
+    # It's probably a good idea to use select() and config_setting
+    # to add different linkopts to BASE_LINKOPTS depending on things
+    # like a "opt" or "dbg" compilation mode.
+    linkopts = [
+        "--bind",       # Enable embind
+        "-sMODULARIZE",
+    ],
+    # This target won't build successfully on its own because of missing emscripten
+    # headers etc. Therefore, we hide it from wildcards.
+    tags = ["manual"],
+)
+
+wasm_cc_binary(
+    name = "hello-embind-wasm",
+    cc_target = ":hello-embind",
+)

bazel/test_external/hello-embind.cc

@@ -0,0 +1,16 @@
+#include <emscripten/bind.h>
+
+using namespace emscripten;
+
+class HelloClass {
+    public:
+    static std::string SayHello(const std::string &name) {
+        return "Yo! " + name;
+    };
+};
+
+EMSCRIPTEN_BINDINGS(Hello) {
+    emscripten::class_<HelloClass>("HelloClass")
+        .constructor<>()
+        .class_function("SayHello", &HelloClass::SayHello);
+}