Mark pregenerated/ to be ignored for the repository's language statistics

Author: wroyca

.gitattributes

@@ -17,3 +17,9 @@
 # Use `binary` to make sure certain files are never auto-detected as text.
 #
 #*.png binary
+
+# Use `linguist-generated` attribute to mark or unmark paths to be ignored for
+# the repository's language statistics and hidden by default in diffs.
+#
+hello/hello/pregenerated/** linguist-generated=true
+hello/doc/pregenerated/** linguist-generated=true