Add documentation for new shrink_host feature in bti-shrink-urls.

Document the configuration of bti-shrink-urls in bti-shrink-urls.xml,
bti.xml, and add a commented out example to bti.example.

bti-shrink-urls.xml

@@ -37,7 +37,7 @@
          bti-shrink-urls converts URLs to a shorter form using a web service.
         </para>
         <para>
-          Currently only http://2tu.us/ is supported.
+          Currently http://2tu.us/ (default) and http://bit.ly / http://j.mp are supported.
         </para>
       </refsect1>
 
@@ -72,6 +72,40 @@
         </variablelist>
       </refsect1>
 
+      <refsect1><title>CONFIGURATION</title>
+        <para>
+         bti-shrink-urls is configured by setting some values in ~/.bti:
+        </para>
+        <variablelist>
+          <varlistentry>
+            <term><option>shrink_host</option></term>
+            <listitem>
+              <para>
+	        Possible values: 2tu.us (default), bit.ly, j.mp
+	      </para>
+            </listitem>
+          </varlistentry>
+          <varlistentry>
+            <term><option>shrink_bitly_login</option></term>
+            <listitem>
+              <para>
+               API login for bit.ly, j.mp, required if shrink_host is set to  bit.ly or j.mp.
+               See https://code.google.com/p/bitly-api/wiki/ApiDocumentation
+              </para>
+            </listitem>
+          </varlistentry>
+          <varlistentry>
+            <term><option>shrink_bitly_key</option></term>
+            <listitem>
+              <para>
+               API key for bit.ly, j.mp, required if shrink_host is set to  bit.ly or j.mp.
+               See https://code.google.com/p/bitly-api/wiki/ApiDocumentation
+              </para>
+            </listitem>
+          </varlistentry>
+        </variablelist>
+      </refsect1>
+
        <refsect1><title>AUTHOR</title>
          <para>Written by Bart Trojanowski <email>bart@jukie.net</email>.</para>
        </refsect1>

bti.example

@@ -13,3 +13,7 @@ logfile=.bti.log
 #user=gregkh
 #proxy=http://localhost:8080
 #shrink-urls=yes
+# Example of using bit.ly in bti-shrink-urls
+#shrink_host=bit.ly
+#shrink_bitly_login=bitlyuser
+#shrink_bitly_key=R_deadbeef

bti.xml

@@ -169,7 +169,11 @@
                 more suitable for micro-blogging.
               </para>
               <para>
-                Currently, only http://2tu.us/ is used as a URL shrinking service.
+                The following URL shrinking services are available:
+                http://2tu.us/ (default) and http://bit.ly / http://j.mp
+              </para>
+              <para>
+                See the documentation for bti-shrink-urls for the configuration options.
               </para>
             </listitem>
           </varlistentry>