Add misc. files to gitattributes

There are a handful of repository specific config and info files still downloaded with a fresh `composer install` of this package, these are now ignored

.gitattributes

@@ -3,9 +3,13 @@ bin/ export-ignore
 docs/ export-ignore
 examples/ export-ignore
 tests/ export-ignore
+.codecov.yml export-ignore
 .coveralls.yml export-ignore
 .gitignore export-ignore
 .gitattributes export-ignore
 .phpcs.xml.dist export-ignore
 .travis.yml export-ignore
+CHANGELOG.md export-ignore
 package.xml.tpl export-ignore
+phpunit.xml.dist export-ignore
+README.md export-ignore