ci(update-index.sh): Add a script to update docs/index.md

Related: ocaml-sf#490

Co-authored-by: Erik Martin-Dorel <erik@martin-dorel.org>

scripts/update-index.sh

@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+
+# This script updates 'docs/index.md' from 'README.md',
+# and changes github.com/…/learn-ocaml/…/docs URLs to relative paths,
+# so that github.io pages work independently of github.com src files.
+
+srcdir=$(cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null && pwd)
+
+readme=$(readlink -f "$srcdir/../README.md")
+index=$(readlink -f "$srcdir/../docs/index.md")
+
+if [[ ! -r "$readme" ]]
+then
+  echo "Error: '$readme': file does not exist or is unreadable"
+  exit 1 
+fi
+
+if [[ ! -w "$index" ]]
+then
+  echo "Error: '$index': file does not exist or is not writable"
+  exit 1 
+fi
+
+url="https://github.com/ocaml-sf/learn-ocaml/blob/master/docs"
+
+sed -e "s;$url;.;g" "$readme" > "$index"