Add more detailed description on zbMATH

[ibe-314]

I added a more detailed description of the zbMATH Search. Furthermore, I added information for the id based search via zbMATH JabRef/jabref#7298.

[mlep]

These examples are directly taken from the help page of zbmath.org. I believe we are not allowed to do so (because of copyright). Please, provide new examples or link to the zbmath help page.

[ibe-314]

I deleted the examples that where taken from the zbmath help page and added some new ones.

[ibe-314]

Hi, the new complex search in JabRef 5.2 does not support the zbmath fields. Thus the structured query I described in this PR does not work anymore with JabRef 5.2 (but they work with 5.1), see JabRef/jabref#7298. I will change my PR accordingly. Is there a description of the new JabRef query syntax? Then I could test which zbmath fields still work.

[koppor]

@DominikVoigt Could you provide a quick pointer to @ibe-314? I did not found a PR on the complex search here... Maybe, we need to add some supported terms?

[koppor]

@ibe-314 You can leave your PR open. I just flag it as "draft" meaning "work in progress". This allows it to be easy discoverable.

[koppor]

@ibe-314 Thank you for the pull request. @DominikVoigt and I prioritist our work and work on a refined implementation of our queries. We will support zbMath from the beginning. We will update the documentation accordingly. Thereby, we will use your pull request as basis. Nothing left todo on your side.

[koppor]

I merged the text into the PR #348. I adapted the text to our new general search syntax.

#### Structured Search

You cannot use the same query syntax as in the one-line search at zbmath.org;
you have to stick with the Apache Lucence syntax.
 This means that your query can be composed of several terms, combined by the logical operators ` AND ` and ` OR `.
 Queries are case-insensitive. Further operators that can be used are ` NOT` for logical negation,
 `*` for a right wildcard, `" "` for exact phrase matches, and parentheses `( )` to group terms.
 Optionally, it is possible to add a field name in the form field:text to limit the search results. The supported fields are:

| field | description |
| -- | -- |
| `author` | Author, editor - sent in the `au` field |
| `title` | Author, editor - sent in the `ti` field |
| `journal` | Journal - sent in the `so` field |
| `year` | Year - sent in the `py` field |
| `yearrange` | Year range - sent in the `py` field |
| `cc` | MSC code |
| `dt` | document type (possible values are `j` for journal articles, `b` for books, `a` for book articles) |
| `an` | the zbl id of the document |
| `ai` | internal author identifier |
| `la` | language either as a string or as [ISO 639-1](https://en.wikipedia.org/wiki/ISO_639-1) language code |
| `ab` | search for term in reviews or abstracts |
| `rv` | reviewer |
| `sw` | software |
| `en` | external identifier |
| `br` | biographical reference |

#### Examples

* [`algebra*](https://zbmath.org/?q=algebra*): Searches for publications containing a term starting with algebra (e.g. algebra, algebras, algebraic, etc.) in any field.
* [`title:"Graph Theory"`](https://zbmath.org/?q=ti%3A+%E2%80%9CGraph+Theory%E2%80%9D): Searches for publications with the exact phrase *Graph Theory* in their `title` field.
* [`an:0492.90056`](https://zbmath.org/?q=an%3A0492.90056): Searches for the document with zbl number *0492.90056*.
* [`author:Berge and title:"Graph Theory"`](https://zbmath.org/?q=au%3A+Berge+%26+ti%3A+%E2%80%9CGraph+Theory%E2%80%9D): Searches for entries written by *Berge* with `Graph Theory` in their **title** field. The **and-operator &** is default and can be omitted.
* [`dt:b author:Berge`](https://zbmath.org/?q=dt%3A+b+au%3A+Berge): Searches for all books written by Berge.
* [`title:"Graph Theory" yearrange:2010-2020`](https://zbmath.org/?q=ti%3A+%E2%80%9CGraph+Theory%E2%80%9D+py%3A+2010-2020): Searches for documents containing the exact phrase `Graph Theory` in their **title** that are published between *2010* and *2020*.
* [`so:Combinatorica`](https://zbmath.org/?q=so%3A+Combinatorica): Searches for documents published in the journal `Combinatorica`.
* [`cc:"(05C|90C)"`](https://zbmath.org/?q=cc%3A+%2805C%7C90C%29): Searches for documents with **MSC code** in `05C` or `90C`.
* [`la:"es | pt"`](https://zbmath.org/?q=la%3A+es+%7C+pt): Searches for documents written in Spanish or Portuguese.
* [`sw:python`](https://zbmath.org/?q=sw%3Apython): Searches for publications using the **software** `python`.
* [`en:arXiv`](https://zbmath.org/?q=en%3AarXiv): Searches for entries with a link to an `arXiv` preprint.
* [`br:"Claude Berge"`](https://zbmath.org/?q=br%3AClaude+Berge): Searches for publications with biographical information on `Claude Berge`.