Generated files have an execution permissions on Linux

[Dmitry Volodin]

When utilizing embedding and file created by gomarkdoc itself, the file will have execution (+x) permissions for user, group and all, i.e.

11:05 $ ls -la
total 36
drwxrwxr-x 2 dvolodin dvolodin 4096 Jul  4 10:34 .
drwxrwxr-x 3 dvolodin dvolodin 4096 Jul  4 10:34 ..
-rw-rw-r-- 1 dvolodin dvolodin 6184 Jul  4 10:34 helm-client.md
-rwxrwxr-x 1 dvolodin dvolodin 3786 Jul  4 10:34 provider-builder.md

generation with:

gomarkdoc ./provider/impl/v1alpha1/ --repository.default-branch $(DEFAULT_BRANCH) -e -o docs/user-guide/provider-builder.md