Update debug-memory-leak to add now needed step (#47291)

Author: stowen-msft

docs/core/diagnostics/debug-memory-leak.md

@@ -56,6 +56,13 @@ The output should be similar to:
 4807 DiagnosticScena /home/user/git/samples/core/diagnostics/DiagnosticScenarios/bin/Debug/netcoreapp3.0/DiagnosticScenarios
 ```
 
+> [!NOTE]
+> If the previous command doesn't work or isn't found, you likely need to install the `dotnet-counters` tool first. Use the following command:
+>
+> ```console
+> dotnet tool install --global dotnet-counters
+> ```
+
 Now, check managed memory usage with the [dotnet-counters](dotnet-counters.md) tool. The `--refresh-interval` specifies the number of seconds between refreshes:
 
 ```console