add src folder to .gitignore

When adding the [api-connection-manager](https://github.com/daithi-coombes/api-connection-manager) and the [api-con-mngr-modules](https://github.com/daithi-coombes/api-con-mngr-modules) to the `src/public/wp-content/plugins` folder they are added as changes in git.

my vote would be to add the `src` folder to .gitignore as all files in the `src` folder are editable by the developer