Add possible values to logLevel setting

This change adds the possible set of values for the logLevel setting so
that the user knows which log levels are available for use.

Author: daviwil

package.json

@@ -190,7 +190,7 @@
                 "powershell.developer.editorServicesLogLevel": {
                     "type": "string",
                     "default": "Normal",
-                    "description": "Sets the logging verbosity level for the PowerShell Editor Services host executable."
+                    "description": "Sets the logging verbosity level for the PowerShell Editor Services host executable.  Possible values are 'Verbose', 'Normal', 'Warning', and 'Error'"
                 },
                 "powershell.developer.editorServicesWaitForDebugger": {
                     "type": "boolean",