HS stats: Add changes file and improve man page.

changes/feature13192

@@ -0,0 +1,13 @@
+m  o Major features (hidden services):
+    - Add a HiddenServiceStatistics option that allows Tor relays to
+      gather and publish statistics about hidden service usage, to
+      better understand the size and volume of the hidden service
+      network. Specifically, if a Tor relay is an HSDir it will
+      publish the approximate number of hidden services that have
+      published descriptors to it the past 24 hours. Also, if a relay
+      has acted as a hidden service rendezvous point, it will publish
+      the approximate amount of rendezvous cells it has relayed the
+      past 24 hours. The statistics themselves are obfuscated so that
+      the exact values cannot be derived. For more details see
+      proposal 238 "Better hidden service stats from Tor relays". This
+      feature is currently disabled by default. Implements feature 13192.

doc/tor.1.txt

@@ -1765,9 +1765,11 @@ is non-zero):
     of connections to disk every 24 hours. (Default: 0)
 
 [[HiddenServiceStatistics]] **HiddenServiceStatistics** **0**|**1**::
-    When this option is enabled, a Tor relay writes statistics on its role as
-    hidden-service directory, introduction point, or rendezvous point to disk
-    every 24 hours. (Default: 0)
+    When this option is enabled, a Tor relay writes obfuscated
+    statistics on its role as hidden-service directory, introduction
+    point, or rendezvous point to disk every 24 hours. If
+    ExtraInfoStatistics is also enabled, these statistics are further
+    published to the directory authorities. (Default: 0)
 
 [[ExtraInfoStatistics]] **ExtraInfoStatistics** **0**|**1**::
     When this option is enabled, Tor includes previously gathered statistics in