feature(petition): added text petition

src/PetitionText.php

+<?php
+
+namespace WPDesk\RepositoryRating;
+
+/**
+ * Petition text generator.
+ */
+interface PetitionText {
+
+	/**
+	 * Returns petition text.
+	 *
+	 * @return string
+	 */
+	public function get_petition_text(): string;
+
+}
\ No newline at end of file