Add gitattributes (#1528)

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Co-authored-by: Kuba Werłos <werlos@gmail.com>

Author: theofidry

.gitattributes

@@ -0,0 +1,15 @@
+/.* export-ignore
+/dist/ export-ignore
+/fixtures/ export-ignore
+/requirement-checker/ export-ignore
+/tests/ export-ignore
+/vendor-bin/ export-ignore
+/composer.lock export-ignore
+/infection.json.dist export-ignore
+/Makefile export-ignore
+/Makefile.e2e export-ignore
+/mkdocs.yaml export-ignore
+/phpbench.json export-ignore
+/phpunit.xml.dist export-ignore
+/rector.php export-ignore
+/scoper.inc.php export-ignore