Update Buck C++ sample to demonstrate multiple "platforms" in .buckconfig (fbsamples#10)

* Demonstrate user-defined platform flavors with a platform called `other_platform`

* Add a `.gitignore` that includes Buck artifacts to ignore

* Update README to use `--show-output` instead of explicitly stating the path to the output

Author: carljparker

.gitignore

@@ -0,0 +1,4 @@
+# Buck
+buck-out
+.buckconfig.local
+.buckd

hello-buck-cxx/.buckconfig

@@ -0,0 +1,7 @@
+
+[cxx]
+  cxxppflags="-D HELLOSTRING=\"Buck\""
+
+[cxx#other_platform]
+  cxxppflags="-D HELLOSTRING=\"Chuck\""
+

hello-buck-cxx/README.md

@@ -1,19 +1,29 @@
 
 To build using buck:
 
-    buck build :main
+    buck build --show-output :main
 
-The executable, `main` will be in `./buck-out/gen`.
+The `--show-output` option shows the path to the output from the build.
+
+To build and run using buck:
+
+    buck run :main
+
+To build and run using the alternative `#other_platform` platform
+defined in `.buckconfig`:
+
+    buck run :main#other_platform
 
 You can also build any of the following flavors:
 
     buck build :main#strip-debug
     buck build :main#strip-non-global
     buck build :main#strip-all
 
-For a description of these flavors, see the Buck documentation at the following URL:
+For a description of these flavors, see the Buck documentation at the
+following URL:
 
-<https://buckbuild.com/rule/cxx_binary.html>
+>  <https://buckbuild.com/rule/cxx_binary.html>
 
 
 **End of README.md**

hello-buck-cxx/hello-string.cxx

@@ -1,7 +1,10 @@
 #include "stdio.h"
 #include "hello-string.h"
 
-const char * hello_string::HELLO = "Buck";
+//
+// HELLOSTRING is defined in .buckconfig
+//
+const char * hello_string::HELLO = HELLOSTRING;
 
 hello_string::hello_string() {};