Document feedhq-url setting

It's been around since 5ca3bbe, but
wasn't documented back then. Since FeedHQ is open source and its
instances can be self-hosted, there's no reason to hide this setting
from the users.

Kudos to flips on IRC, whose question led to this commit.

doc/configcommands.dsv

@@ -33,6 +33,7 @@ feedhq-password|<password>|""|This variable sets your FeedHQ password for FeedHQ
 feedhq-passwordfile|<path-to-file>|""|A more secure alternative to the above, by storing your password elsewhere in your system.|feedhq-passwordfile "path-to-file"
 feedhq-passwordeval|<command>|""|Another secure alternative, is providing your password from an external command that is evaluated during login. This can be used to read your password from a gpg encrypted file or your system keyring.|feedhq-passwordeval "command some-parameter"
 feedhq-show-special-feeds|[yes/no]|yes|If this is set, then "special feeds" like "People you follow" (articles shared by people you follow), "Starred items" (your starred articles) and "Shared items" (your shared articles) appear in your subscription list.|feedhq-show-special-feeds "no"
+feedhq-url|<url>|"https://feedhq.org/"|Configures the URL where your FeedHQ instance resides.|feedhq-url "https://feedhq.example.com/"
 feedlist-format|<format>|"%4i %n %11u %t"|This variable defines the format of entries in the feed list. See the respective section in the documentation for more information on format strings.|feedlist-format " %n %4i - %11u -%> %t"
 feedlist-title-format|<format>|"N %V - Your feeds (%u unread, %t total)%?T? - tag `%T'&?"|Format of the title in feed list. See "Format Strings" section of Newsbeuter manual for details on available formats.|feedlist-title-format "Feeds (%u unread, %t total)"
 filebrowser-title-format|<format>|"%N %V - %?O?Open File&Save File? - %f"|Format of the title in file browser. See "Format Strings" section of Newsbeuter manual for details on available formats.|N %V - %?O?Open File&Save File? - %f|filebrowser-title-format "%?O?Open File&Save File? - %f"

doc/example-config

@@ -412,6 +412,16 @@
 #
 # feedhq-show-special-feeds "no"
 
+####  feedhq-url
+#
+# Configures the URL where your FeedHQ instance resides.
+#
+# Syntax: <url>
+#
+# Default value: "https://feedhq.org/"
+#
+# feedhq-url "https://feedhq.example.com/"
+
 ####  feedlist-format
 #
 # This variable defines the format of entries in the feed list. See the

doc/newsbeuter.txt

@@ -615,6 +615,10 @@ instead of +"+.)
 
 See also <<_passwords_for_external_apis,feedhq-passwordfile and feedhq-passwordeval>>.
 
+if you're using a standalone instance, you should add one more setting:
+
+    feedhq-url "https://the.url.of/your/feedhq/instance"
+
 When you start newsbeuter, it will download the feeds that you configured
 in FeedHQ. Please take a closer look at the configuration commands for what 
 you can configure in newsbeuter regarding FeedHQ.