Improve the docs

• In tools.md, section "Using the command-line interface": "The command-line interface is provided by the scripts located in the scripts folder." should be deleted or replaced by "The command-line interface is invoked with the command texts.".
• In index.rst: "Have a look at the use cases, available in the folder, to get a first impression:" Which folder?
• In this section: the launchpad parameter is only used if type is gridfs. This should be explained. And it should be explained that the attributes are specific to the objects stored in the datastore but not global for the model.
• In this section: Add some info about the RESCONFIG_LOC environment variable.
• In this section: Add the %find magic to the table.
• In https://vre-language.readthedocs.io/en/latest/query.html#the-find-command insert links to https://vre-language.readthedocs.io/en/latest/query.html#the-tag-statement when refering to tag statement.