[clangd] Give an example for global-symbol-builder usage

[kbobyrev]

Summary

global-symbol-builder help message mentions -executor=<string> option, but doesn't give any example of what the value could be

Assuming the most popular use case to be building the whole project index, help message should probably give an example of such usage.

[ioeric]

clang-tools-extra/clangd/global-symbol-builder/GlobalSymbolBuilderMain.cpp

153

why replace char * with auto? I'd keep char * as it's clearer and short enough.

158

Maybe also give an example for running on one file?

[kbobyrev]

Addressed two comments, added an example of running the tool over a number of source files without providing compile_commands.json; added a note about collecting files from headers only.

clang-tools-extra/clangd/global-symbol-builder/GlobalSymbolBuilderMain.cpp

 
 } // namespace
 } // namespace clangd
 } // namespace clang
 
 int main(int argc, const char **argv) {
   llvm::sys::PrintStackTraceOnErrorSignal(argv[0]);
 
-  const char* Overview =
-      "This is an **experimental** tool to generate YAML-format "
-      "project-wide symbols for clangd (global code completion). It would be "
-      "changed and deprecated eventually. Don't use it in production code!";
+  const auto Overview = R"(
+  This is an **experimental** tool to generate YAML-format project-wide symbols
+  for clangd (global code completion). It would be changed and deprecated
+  eventually. Don't use it in production code!
+
+  Example usage for building index for the whole project:
+
+  $ global-symbol-builder --executor=all-TUs compile_commands.json > index.yaml
+  )";
+
   auto Executor = clang::tooling::createExecutorFromCommandLineArgs(
       argc, argv, cl::GeneralCategory, Overview);
 
   if (!Executor) {
     llvm::errs() << llvm::toString(Executor.takeError()) << "\n";
     return 1;
   }