Add note about running dotnet-format only against trusted code

Author: dibarbet

docs/core/tools/dotnet-format.md

@@ -34,6 +34,9 @@ dotnet format -h|--help
 
 The MSBuild project or solution to run code formatting on. If a project or solution file is not specified, MSBuild searches the current working directory for a file that has a file extension that ends in *proj* or *sln*, and uses that file.
 
+> [!WARNING]
+> dotnet-format may restore, compile, and run analyzers on the specified project or solution.  Make sure to only invoke the tool against trusted code.
+
 ## Options
 
 None of the options below are required for the `dotnet format` command to succeed, but you can use them to further customize what is formatted and by which rules.