Shared link expiration backend

Redirect from sign in page when user is logged
Updated README.md

database/migrations/2020_08_25_143449_add_expiration_at_attribute_to_shares_table.php

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+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+class AddExpirationAtAttributeToSharesTable extends Migration
+{
+    /**
+     * Run the migrations.
+     *
+     * @return void
+     */
+    public function up()
+    {
+        Schema::table('shares', function (Blueprint $table) {
+            $table->integer('expire_in')->after('password')->nullable();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     *
+     * @return void
+     */
+    public function down()
+    {
+        Schema::table('shares', function (Blueprint $table) {
+            //
+        });
+    }
+}