add a help section for the syntastic_auto_jump option

doc/syntastic.txt

@@ -133,6 +133,12 @@ errors: >
     let g:syntastic_enable_signs=1
 <
 
+                                                       *'syntastic_auto_jump'*
+Enable this option if you want the cursor to jump to the first detected error
+when saving or opening a file: >
+    let g:syntastic_auto_jump=1
+<
+
                                                    *'syntastic_auto_loc_list'*
 Use this option to tell syntastic to automatically open the |location-list|
 (see |syntastic-error-window|) when a buffer has errors: >