add a library (apiapp) section missing in the doc

[panaC]

There are a section to add an opds feed (https://thorium.edrlab.org/docs/220_organizing/222_catalogs/) but nothing to add a french library with ApiAPP protocol.

Need to add a french documentation to target french users of these library services

[gautierchomel]

Available in the (soon to be released) french epub: https://github.com/edrlab/thorium-reader-doc/blob/epub-doc/epub-doc/fr/src/pages/111_catalogs_actions.md#cr%C3%A9er-un-compte-dans-une-biblioth%C3%A8que-publique-fran%C3%A7aise