DOC: configuration: httpclient global option

Documentation about the 4 options in the global section for the
httpclient:

- httpclient.ssl.verify
- httpclient.ssl.ca-file
- httpclient.resolvers.id
- httpclient.resolvers.prefer
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 3290532..990b837 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -1487,6 +1487,43 @@
   See "h1-case-adjust", "option h1-case-adjust-bogus-client" and
   "option h1-case-adjust-bogus-server".
 
+httpclient.ssl.ca-file <cafile>
+  This option defines the ca-file which should be used to verify the server
+  certificate. It takes the same parameters as the "ca-file" option on the
+  server line.
+
+  By default and when this option is not used, the value is
+  "@system-ca" which tries to load the CA of the system. If it fails the SSL
+  will be disabled for the httpclient.
+
+  However, when this option is explicitly enabled it will trigger a
+  configuration error if it fails.
+
+httpclient.ssl.verify [none|required]
+  Works the same way as the verify option on server lines. If specified to 'none',
+  servers certificates are not verified. Default option is "required".
+
+  By default and when this option is not used, the value is
+  "required". If it fails the SSL will be disabled for the httpclient.
+
+  However, when this option is explicitly enabled it will trigger a
+  configuration error if it fails.
+
+httpclient.resolvers.id <resolvers id>
+  This option defines the resolvers section with which the httpclient will try
+  to resolve.
+
+  Default option is the "default" resolvers ID. By default, if this option is
+  not used, it will simply disable the resolving if the section is not found.
+
+  However, when this option is explicitly enabled it will trigger a
+  configuration error if it fails to load.
+
+httpclient.resolvers.prefer <ipv4|ipv6>
+  This option allows to chose which family of IP you want when resolving,
+  which is convenient when IPv6 is not available on your network. Default
+  option is "ipv6".
+
 insecure-fork-wanted
   By default HAProxy tries hard to prevent any thread and process creation
   after it starts. Doing so is particularly important when using Lua files of