mentioning pid processor in README #165

README.mdown

@@ -183,6 +183,7 @@ Processors
 - _WebProcessor_: Adds the current request URI, request method and client IP to a log record.
 - _MemoryUsageProcessor_: Adds the current memory usage to a log record.
 - _MemoryPeakUsageProcessor_: Adds the peak memory usage to a log record.
+- _ProcessIdProcessor_: Adds the process id to a log record.
 
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