Update sample config file.

This commit adds a couple of options which were not details in the sample
config file.  It also fixes a couple of typos and makes the example default
maxpeers setting in the config file match the actual default used in btcd.

sample-btcd.conf

@@ -29,15 +29,30 @@
 ; proxypass=
 
 ; The SOCKS5 proxy above is assumed to be Tor (https://www.torproject.org).
-; If the proxy  is not tor the the following my be used to prevent using
-; tor specific SOCKS queries to lookup addresses (this increases anonymity when
-; tor is used by preventing your IP being leaked via DNS).
+; If the proxy is not tor the following may be used to prevent using tor
+; specific SOCKS queries to lookup addresses (this increases anonymity when tor
+; is used by preventing your IP being leaked via DNS).
 ; noonion=1
 
 ; Use an alternative proxy to connect to .onion addresses. The proxy is assumed
 ; to be a Tor node. Non .onion addresses will be contacted with the main proxy
 ; or without a proxy if none is set.
 ; onion=127.0.0.1:9051
+; onionuser=
+; onionpass=
+
+; Use Universal Plug and Play (UPnP) to automatically open the listen port
+; and obtain the external IP address from supported devices.  NOTE: This option
+; will have no effect if exernal IP addresses are specified.
+; upnp=1
+
+; Specify the external IP addresses your node is listening on.  One address per
+; line.  btcd will not contact 3rd-party sites to obtain external ip addresses.
+; This means if you are behind NAT, your node will not be able to advertise a
+; reachable address unless you specify it here or enable the 'upnp' option (and
+; have a supported device).
+; externalip=1.2.3.4
+; externalip=2002::1234
 
 ; ******************************************************************************
 ; Summary of 'addpeer' versus 'connect'.
@@ -81,7 +96,7 @@
 ; connect=[fe80::2]:8333
 
 ; Maximum number of inbound and outbound peers.
-; maxpeers=8
+; maxpeers=125
 
 ; How long to ban misbehaving peers. Valid time units are {s, m, h}.
 ; Minimum 1s.
@@ -206,7 +221,7 @@
 ; blockminsize=0
 
 ; Specify the maximum block size in bytes to create.  This value will be limited
-; to the consensus limit if it is larger than this value.
+; to the consensus limit if it is larger than that value.
 ; blockmaxsize=750000
 
 ; Specify the size in bytes of the high-priority/low-fee area when creating a