Improve error message and tooltip

Provide a clearer error message if no direction has been selected and
also provide better information in the tooltip.

scripts/Interface/ui/sans_isis/beam_centre.ui

@@ -211,7 +211,7 @@
          <item row="13" column="0" colspan="5">
           <widget class="QGroupBox" name="groupBox">
            <property name="toolTip">
-            <string>&lt;html&gt;&lt;head/&gt;&lt;body&gt;&lt;p&gt;Controls in which directions the algorithm will search for the beam centre.&lt;/p&gt;&lt;/body&gt;&lt;/html&gt;</string>
+            <string>&lt;html&gt;&lt;head/&gt;&lt;body&gt;&lt;p&gt;Controls in which directions the algorithm will search for the beam centre. One or more options must be selected.&lt;/p&gt;&lt;/body&gt;&lt;/html&gt;</string>
            </property>
            <property name="title">
             <string>Direction</string>

scripts/SANS/sans/gui_logic/models/async_workers/beam_centre_async.py

@@ -63,7 +63,7 @@ def find_beam_centre(self, state: AllStates, settings: BeamCentreFields) -> Opti
         """
         centre_finder = SANSCentreFinder()
         if not settings.find_direction:
-            self._logger.error("Have chosen no find direction exiting early")
+            self._logger.error("No direction has been selected - please select either one or both of the Direction checkboxes.")
             raise ValueError("Unable to run beam centre finder as no direction settings have been provided.")
 
         pos_1 = settings.lab_pos_1 if settings.component is DetectorType.LAB else settings.hab_pos_1