Docs: fix some typos in config.rst

[garenchan]

Fix some typos in config.rst

[davidism]

Please make docs changes against 1.0-maintenance (unless they have to do with new features). Otherwise the changes will only appear in the dev version of the docs.

[garenchan]

@davidism, do you mean that document related PR should be based on the 1.0-maintenance branch?

[davidism]

Yes

[garenchan]

There are some docs changes in the dev version that are also useful for 1.0-maintenance. If these commits aren't merged into 1.0-maintenance, the next change will be cumbersome.

[davidism]

I know, I'm working on cherry picking them.

[garenchan]

Thank you for your hard work!