Add git attributes

Author: adriansuter

.gitattributes

@@ -0,0 +1,14 @@
+# Enforce Unix newlines
+* text=lf
+
+# Exclude unused files
+# see: https://redd.it/2jzp6k
+/tests              export-ignore
+/.gitattributes     export-ignore
+/.gitignore         export-ignore
+/.travis.yml        export-ignore
+/CONTRIBUTING.md    export-ignore
+/phpcs.xml.dist     export-ignore
+/phpstan.neon.dist  export-ignore
+/phpunit.xml.dist   export-ignore
+/README.md          export-ignore