Add README for AutoTxDiagnostics

Refers to #53

ATxDiagnostics/README.md

+# AutoTx Diagnostics
+
+The `AutoTxDiagnostics` tool can be used to show some diagnostics information
+and continously print performance monitoring messages to the console. With the
+latter it allows to investigate performance-critical situations without the need
+to actually run the `AutoTx` service itself.
+
+## Basic Usage
+
+By default, the log level for messages is set to *Debug* and ***all*** available
+performance monitors will be enabled. For this, simply run the tool:
+
+```
+.\AutoTxDiagnostics.exe
+```
+
+## Advanced Usage
+
+To run the tool with log level *Trace*, simply add `trace` as the first
+parameter on the command line when starting:
+
+```
+.\AutoTxDiagnostics.exe trace
+```
+
+The second parameter can be used to explicitly request a specific combination of
+performance monitors to be active. To run for example only the *Disk I/O*
+monitoring, start the tool like this:
+
+```
+.\AutoTxDiagnostics.exe trace PhysicalDisk
+```
+
+Combinations of monitors have to be separated by a comma, for example:
+
+```
+.\AutoTxDiagnostics.exe trace PhysicalDisk,CPU
+```
+
+## Exit Codes
+
+The diagnostics tool can be terminated by pressing `Ctrl+C`.
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