maint: document release procedure

* maint/README-release: New file.
* maint/gen-release-notes.sh: Likewise.
* maint/gen-release-github.sh: Likewise.
* maint/gen-release-gitlab.sh: Likewise.

Author: ldv-alt

maint/README-release

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+* commit changes prepared by maint/update_copyright_years.sh
+* update copyright year number range in COPYING and debian/copyright
+* prepare NEWS for release
+* generate release notes for strace.io and git repository mirrors
+  using maint/gen-release-notes.sh, maint/gen-release-github.sh
+  and maint/gen-release-gitlab.sh
+* create a release tag using maint/gen-tag-message.sh
+* generate a release tarball using make-dist
+* send the tarball to release farms for the final testing
+* prepare and test package builds for ALT and Rawhide
+* generate a detached signature for the tarball using gpg -ab
+* push the release tag to all git repository mirrors
+* upload the tarball, it's signature and release notes to strace.io
+  and all git repository mirrors
+* adjust the link to the latest release at strace.io
+* submit a release announce to strace-devel
+* update irc #strace topic using /topic #strace
+* update https://en.wikipedia.org/wiki/Strace
+* tweet the news
+* announce the new release at http://freshcode.club/projects/strace
+* announce the new release at other news-related sites

maint/gen-release-github.sh

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+#!/bin/sh -efu
+
+"$(dirname "$0")"/gen-tag-message.sh |
+	sed 's/\([^[:space:]]\)\*/\1\\*/g'
+
+cat <<'EOF'
+
+Downloads
+=========
+
+**Please ignore so called "Source code" links provided by github above, they are useless**.
+EOF

maint/gen-release-gitlab.sh

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+#!/bin/sh -efu
+
+cat <<'EOF'
+Downloads
+=========
+
+EOF
+
+set +f
+set -- strace-*.tar.xz*
+set -f
+for f; do
+	printf '[%s](/uploads/%s/%s)\n' "$f" "..." "$f"
+done
+
+cat <<'EOF'
+**Please ignore so called "Source code" links provided by gitlab, they are useless**.
+
+EOF
+
+"$(dirname "$0")"/gen-tag-message.sh |
+	sed 's/\([^[:space:]]\)\*/\1\\*/g'

maint/gen-release-notes.sh

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+#!/bin/sh -efu
+
+echo '<pre>'
+"$(dirname "$0")"/gen-tag-message.sh
+echo '</pre>'