document preconditions for 'got backout'
diff --git a/got/got.1 b/got/got.1
index ccaccdb..524d8ee 100644
--- a/got/got.1
+++ b/got/got.1
@@ -444,6 +444,13 @@ committed with
or discarded again with
.Cm got revert .
.Pp
+.Cm got backout
+will refuse to run if certain preconditions are not met.
+If the work tree contains multiple base commits it must first be updated
+to a single base commit with
+.Cm got update .
+If the work tree already contains files with merge conflicts, these
+conflicts must be resolved first.
.El
.Sh ENVIRONMENT
.Bl -tag -width GOT_AUTHOR