minor #405 Add .gitattributes file (ker0x)

This PR was merged into the master branch.

Discussion
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Add .gitattributes file

This will prevent to download unnecessary files when installing the package!

Commits
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c40e619 Add .gitattributes file

.gitattributes

@@ -0,0 +1,8 @@
+/.github                    export-ignore
+/bin                        export-ignore
+/tests                      export-ignore
+/.gitattributes             export-ignore
+/.gitignore                 export-ignore
+/.php-cs-fixer.dist.php     export-ignore
+/phpstan.neon.dis           export-ignore
+/phpunit.xml.dist           export-ignore