Added .gitattributes (symfony#100)

* Added .gitattributes

* Removed README.md from ignored file

Author: alexmanno

.gitattributes

@@ -0,0 +1,10 @@
+/examples/ export-ignore
+/appveyor.yml export-ignore
+/panther.png export-ignore
+/.php_cs.dist export-ignore
+/phpstan.neon export-ignore
+/phpunit.xml.dist export-ignore
+/tests/ export-ignore
+/.travis.yml export-ignore 
+/.gitignore export-ignore
+/.gitattributes export-ignore