Add C and C++ to README

Author: parlough

README.md

@@ -48,6 +48,8 @@ void main() {
 Currently the following languages are supported with
 the specified default and alternative IDs:
 
+- C (`c`)
+- C++ (`cpp`)
 - Dart (`dart`)
 - Groovy (`groovy`, `gradle`)
 - HTML (`html`)

test/goldens/c/hello-world.out

@@ -1,6 +1,10 @@
 #include <stdio.h>
-^^^^^^^^^^^^^^^^^^
-source-code-c-metadata-preprocessor
+^
+source-code-c-metadata-preprocessor-directive-punctuation
+ ^^^^^^^
+ source-code-c-metadata-preprocessor-directive-metadata-preprocessor-directive-name
+        ^^^^^^^^^^
+        source-code-c-metadata-preprocessor-directive-metadata-preprocessor-directive-options
 
 const char* message = "Hello, world!";
 ^^^^^