Add scripts/fix-dco.sh (#1303)

Use it as parameter to git-filter-branch
Read the docs git help filter-branch before using it.
Example:
  git filter-branch --msg-filter $PWD/scripts/fix-dco.sh -f -- HEAD~69..HEAD

Signed-off-by: kuvaldini <ivan@kuvaldini.pro>

scripts/fix-dco.sh

@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+
+## Use it as parameter to git-filter-branch
+## Read the docs git help filter-branch before using it.
+## Example:
+##   git filter-branch --msg-filter $PWD/scripts/fix-dco.sh -f -- HEAD~69..HEAD
+
+cat >msg
+cat msg
+sigo="Signed-off-by: $GIT_AUTHOR_NAME <$GIT_AUTHOR_EMAIL>";
+if grep -q "^$sigo" msg >&2 ;then
+	echo >&2 "already signed";
+else
+	echo;
+	echo "$sigo";
+fi;