Add tarpaulin.toml configuration file example

[basvandriel]

This pull request adds a example configuration file, based on the src/config/mod.rs file. This is for better readability. I've also added a link to the mod.rs file.

[xd009642]

It's quite a lot of vertical space in the readme. Instead could you merge all the default fields that aren't already in https://github.com/xd009642/tarpaulin/blob/develop/tarpaulin.toml into there and retain the comments and just link people to the existing toml that the project uses 👀

[basvandriel]

It's quite a lot of vertical space in the readme. Instead could you merge all the default fields that aren't already in https://github.com/xd009642/tarpaulin/blob/develop/tarpaulin.toml into there and retain the comments and just link people to the existing toml that the project uses 👀

Done! The null values have been commented out, since this gave syntax errors in the file.