Introduce --dep_roots flag to Stardoc to search alternate roots for bzl deps

This is necessary to handle generated bzl input files.

See https://github.com/bazelbuild/skydoc/issues/151 for details.

RELNOTES: None.
PiperOrigin-RevId: 233481475
diff --git a/src/main/java/com/google/devtools/build/skydoc/SkydocOptions.java b/src/main/java/com/google/devtools/build/skydoc/SkydocOptions.java
index aa561f5..1a45913 100644
--- a/src/main/java/com/google/devtools/build/skydoc/SkydocOptions.java
+++ b/src/main/java/com/google/devtools/build/skydoc/SkydocOptions.java
@@ -47,4 +47,13 @@
       effectTags = OptionEffectTag.UNKNOWN,
       help = "The path of the file to output documentation into")
   public List<String> symbolNames;
+
+  @Option(
+      name = "dep_roots",
+      allowMultiple = true,
+      defaultValue = "",
+      documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
+      effectTags = OptionEffectTag.UNKNOWN,
+      help = "File path roots to search when resolving transitive bzl dependencies")
+  public List<String> depRoots;
 }