Document connect_timeout in Constructor Details

Previously, this was only documented in the `Overview` section and
missing from https://www.rubydoc.info/github/ruby-ldap/ruby-net-ldap/Net%2FLDAP:initialize

lib/net/ldap.rb

@@ -480,6 +480,8 @@ def self.result2string(code) #:nodoc:
   #   server says it supports them. This is a fix for MS Active Directory
   # * :instrumentation_service => An object responsible for instrumenting
   #   operations, compatible with ActiveSupport::Notifications' public API.
+  # * :connect_timeout => The TCP socket timeout (in seconds) to use when
+  #   connecting to the LDAP server (default 5 seconds).
   # * :encryption => specifies the encryption to be used in communicating
   #   with the LDAP server. The value must be a Hash containing additional
   #   parameters, which consists of two keys: