[docgen] Update docs

skip-checks: true

doc/oil.txt

@@ -373,6 +373,10 @@ select({opts}, {callback})                                            *oil.selec
           {tab}        `nil|boolean` Open the buffer in a new tab
           {close}      `nil|boolean` Close the original oil buffer once
                        selection is made
+          {handle_buffer_callback} `nil|fun(buf_id: integer)` If defined, all
+                       other buffer related options here would be ignored. This
+                       callback allows you to take over the process of opening
+                       the buffer yourself.
       {callback} `nil|fun(err: nil|string)` Called once all entries have been
                  opened