release process: split release.sh into two

This allows the add_cosigner workflow to be done before the website links to new binaries.
(so Emzy or other builders can try to reproduce builds and add signatures before new binaries are fully live)

contrib/add_cosigner

@@ -3,12 +3,15 @@
 # This script is part of the workflow for BUILDERs to reproduce and sign the
 # release binaries. (for builders who do not have sftp access to "electrum-downloads-airlock")
 #
+# env vars:
+# - SSHUSER
+#
+#
 # - BUILDER builds all binaries and checks they match the official releases
 #   (using release.sh, and perhaps some manual steps)
 # - BUILDER creates a PR against https://github.com/spesmilo/electrum-signatures/
 #   to add their sigs for a given release, which then gets merged
-# - SFTPUSER runs `$ electrum/contrib/add_cosigner $BUILDER`
-# - SFTPUSER runs `$ SSHUSER=$SFTPUSER electrum/contrib/upload.sh`
+# - SFTPUSER runs `$ SSHUSER=$SFTPUSER electrum/contrib/add_cosigner $BUILDER`
 # - SFTPUSER runs `$ electrum/contrib/make_download $WWW_DIR`
 # -     $ (cd $WWW_DIR; git commit -a -m "add_cosigner"; git push)
 # - SFTPUSER runs `$ electrum-web/publish.sh $SFTPUSER`
@@ -18,6 +21,7 @@ import re
 import os
 import sys
 import importlib
+import subprocess
 
 
 # cd to project root
@@ -32,7 +36,7 @@ ELECTRUM_VERSION = version_module.ELECTRUM_VERSION
 APK_VERSION = version_module.APK_VERSION
 print("version", ELECTRUM_VERSION)
 
-# GPG names of cosigner
+# GPG name of cosigner
 cosigner = sys.argv[1]
 
 version = version_win = version_mac = ELECTRUM_VERSION
@@ -63,3 +67,6 @@ for shortname, filename in files.items():
     os.system(f"wget -nc {sig_url} -O {sig_path}")
     if os.system(f"gpg --verify {sig_path} {path}") != 0:
         raise Exception(sig_name)
+
+print("Calling upload.sh now... This might take some time.")
+subprocess.check_output(["./contrib/upload.sh", ])