Mark text output in docs

src/docs/userguide/libraries.diviner

@@ -37,6 +37,7 @@ To **create a new libphutil library**:
 
 Now you'll get a prompt like this:
 
+  lang=txt
   No library currently exists at that path...
   The directory '/some/path/libcustom/src' does not exist.
 
@@ -49,6 +50,7 @@ Now you'll get a prompt like this:
 Choose a library name (in this case, "libcustom" would be appropriate) and it
 you should get some details about the library initialization:
 
+  lang=txt
   Writing '__phutil_library_init__.php' to
     '/some/path/libcustom/src/__phutil_library_init__.php'...
   Using library root at 'src'...