Update detector-arguments.md to show correct argument for Python detectors

[mnitchie]

Correct detector-arguments.md to show the correct category for Python detectors. When using Pip:

$ omponent-detection scan --SourceDirectory . --ManifestFile ./output.json --DetectorCategories Pip
[17:29:15 ERR] An error occurred while executing the command
Microsoft.ComponentDetection.Orchestrator.Exceptions.InvalidDetectorCategoriesException: Categories Pip did not match any available detectors.
   at Microsoft.ComponentDetection.Orchestrator.Services.DetectorRestrictionService.ApplyRestrictions(DetectorRestrictions restrictions, IEnumerable`1 detectors)
   at Microsoft.ComponentDetection.Orchestrator.Services.ScanExecutionService.ExecuteScanAsync(ScanSettings settings)
   at Microsoft.ComponentDetection.Orchestrator.Commands.ScanCommand.ExecuteAsync(CommandContext context, ScanSettings settings)
   at Spectre.Console.Cli.CommandExecutor.Execute(CommandTree leaf, CommandTree tree, CommandContext context, ITypeResolver resolver, IConfiguration configuration) in /_/src/Spectre.Console.Cli/Internal/CommandExecutor.cs:line 166

When using Python:

$ component-detection scan --SourceDirectory . --ManifestFile ./output.json --DetectorCategories Python
[17:41:47 INF] Finding components...