Add some more documentation

doc/tor.1.txt

@@ -960,7 +960,10 @@ The following options are useful only for clients (that is, if
 **Tor2webMode** **0**|**1**::
     When this option is set, Tor connects to hidden services
     **non-anonymously**.  This option also disables client connections to
-    non-hidden-service hostnames through Tor.  (Default: 0)
+    non-hidden-service hostnames through Tor. It **must only** be used when
+    running a tor2web Hidden Service web proxy.
+    To enable this option the compile time flag --enable-tor2webmode must be
+    specified. (Default: 0)
 
 SERVER OPTIONS
 --------------

src/or/config.c

@@ -1310,7 +1310,8 @@ options_act(const or_options_t *old_options)
   if (options->Tor2webMode) {
     log_err(LD_CONFIG, "This copy of Tor was not compiled to run in "
             "'tor2web mode'. It cannot be run with the Tor2webMode torrc "
-            "option enabled.");
+            "option enabled. To enable Tor2webMode recompile with the "
+            "--enable-tor2webmode option.");
     return -1;
   }
 #endif