Librarian documentation

[boyska]

Write a documentation for people that will not install the node (that is covered by #66), but just use it to add books, search books, etc.

[boyska]

@nullpointer- , this is for you

[ael-code]

we need to create different section for developers, librarian and users

[boyska]

Mh, actually we decided not to provide documentation for users, because they won't read it anyway. The sections are already present:

https://raw.githubusercontent.com/insomnia-lab/libreant/master/doc/source/index.rst

of course the librerian part is still missing; which is what this issue is about