Updated documentation to include options available

Thanks to input from #23 #50 #55 #64 #67 and PR #56 (Commit #1877d98) for feature previously added but not yet documented.

README.md

@@ -43,6 +43,16 @@ grunt-exec will assume an error has occurred and will abort grunt immediately.
   for multiple allowed exit codes.
 *  __callback__: The callback function passed `child_process.exec`. Defaults to 
   a noop.
+* __options__: Options to provide to `child_process.exec`. [NodeJS Documentation](http://nodejs.org/api/child_process.html#child_process_child_process_exec_command_options_callback)
+  - `cwd` String Current working directory of the child process
+  - `env` Object Environment key-value pairs
+  - `encoding` String *(Default: 'utf8')*
+  - `shell` String Shell to execute the command with *(Default: '/bin/sh' on UNIX, 'cmd.exe' on Windows, The shell should understand the -c switch on UNIX or /s /c on Windows. On Windows, command line parsing should be compatible with cmd.exe.)*
+  - `timeout` Number *(Default: 0)*
+  - `maxBuffer` Number largest amount of data (in bytes) allowed on stdout or stderr - if exceeded child process is killed *(Default: 200\*1024)*
+  - `killSignal` String *(Default: 'SIGTERM')*
+  - `uid` Number Sets the user identity of the process. (See [setuid(2)](http://man7.org/linux/man-pages/man2/setuid.2.html).)
+  - `gid` Number Sets the group identity of the process. (See [setgid(2)](http://man7.org/linux/man-pages/man2/setgid.2.html).)
 
 If the configuration is instead a simple `string`, it will be
 interpreted as a full command itself: