number .travis/ script according to build lifecycle and add README to explain

.travis/lint_06_script.sh

@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+#
+# Copyright (c) 2018 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+#
+# Check for new lines in diff that introduce trailing whitespace.
+
+export LC_ALL=C
+
+if [ "$TRAVIS_EVENT_TYPE" = "pull_request" ]; then
+  test/lint/commit-script-check.sh $TRAVIS_COMMIT_RANGE
+fi
+
+test/lint/git-subtree-check.sh src/crypto/ctaes
+test/lint/git-subtree-check.sh src/secp256k1
+test/lint/git-subtree-check.sh src/univalue
+test/lint/git-subtree-check.sh src/leveldb
+test/lint/check-doc.py
+test/lint/check-rpc-mappings.py .
+test/lint/lint-all.sh
+
+if [ "$TRAVIS_REPO_SLUG" = "bitcoin/bitcoin" -a "$TRAVIS_EVENT_TYPE" = "cron" ]; then
+    while read -r LINE; do travis_retry gpg --keyserver hkp://subset.pool.sks-keyservers.net --recv-keys $LINE; done < contrib/verify-commits/trusted-keys &&
+    travis_wait 50 contrib/verify-commits/verify-commits.py;
+fi