[libFuzzer] Update the documentation regarding environment initialization.

TBR=inferno@chromium.org,metzman@chromium.org

Bug: 539572
Change-Id: Ia8904c035a4a5342bed95763be2fb3d64e168c0f
Reviewed-on: https://chromium-review.googlesource.com/c/1318653
Commit-Queue: Max Moroz <mmoroz@chromium.org>
Reviewed-by: Jonathan Metzman <metzman@chromium.org>
Reviewed-by: Max Moroz <mmoroz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605535}

testing/libfuzzer/getting_started.md

@@ -50,7 +50,7 @@ function:
 #include <stdint.h>
 
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
-  // put your fuzzing code here and use data+size as input.
+  // Put your fuzzing code here and use data+size as input.
   return 0;
 }
 ```
@@ -163,7 +163,12 @@ struct Environment {
   }
 };
 
-Environment* env = new Environment();
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+  static Environment env;
+  
+  // Put your fuzzing code here and use data+size as input.
+  return 0;
+}
 ```
 
 ## Mutating Multiple Inputs