Update documentation

README.md

@@ -7,5 +7,36 @@ Docspell is a personal document organizer. You'll need a scanner to
 convert your papers into PDF files. Docspell can then assist in
 organizing the resulting mess :wink:.
 
-See the [microsite](https://eikek.github.io/docspell/) for more
-information.
+You can associate tags, set correspondends, what a document is
+concerned with, a name, a date and some more. If your documents are
+associated with this meta data, you should be able to quickly find
+them later using the search feature. But adding this manually to each
+document is a tedious task. What if most of it could be done
+automatically?
+
+## How it works
+
+Documents have two main properties: a correspondent (sender or
+receiver that is not you) and something the document is about. Usually
+it is about a person or some thing – maybe your car, or contracts
+concerning some familiy member, etc.
+
+1. You maintain a kind of address book. It should list all possible
+   correspondents and the concerning people/things. This grows
+   incrementally with each *new unknown* document.
+2. When docspell analyzes a document, it tries to find matches within
+   your address book. It can detect the correspondent and a concerning
+   person or thing. It will then associate this data to your
+   documents.
+3. You can inspect what docspell has done and correct it. If docspell
+   has found multiple suggestions, they will be shown for you to
+   select one. If it is not correctly associated, very often the
+   correct one is just one click away.
+
+The set of meta data, that docspell uses to draw suggestions from,
+must be maintained manually. But usually, this data doesn't grow as
+fast as the documents. After a while there is a quite complete address
+book and only once in a while it has to be revisited.
+
+The [documentation](https://eikek.github.io/docspell/) provides for
+more information.