Add query language intro to the docs

Author: ddelemeny

docs/get-started/query-language-intro.md

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+---
+title: Introduction to Quickwit's query language
+sidebar_position: 3
+---
+
+Quickwit allows you to search on your indexed documents using a simple query language. Here's a quick overview.
+
+## Clauses
+
+The main concept of this language is a clause, which represents a simple condition that can be tested against documents. 
+
+### Querying fields
+
+A clause operates on fields of your document. It has the following syntax :
+```
+field: condition
+```
+
+For example, when searching documents where the field `app_name` contains the token `tantivy`, you would write the following clause:
+```
+app_name:tantivy
+```
+
+In many cases the field name can be omitted, quickwit will then use the `default_search_fields` configured for the index.
+
+### Adressing structured data
+
+Data stored deep inside nested data structures like `object` or `json` fields can be addressed using dots as separators in the field name.
+For instance, the document `{"product": {"attributes": {color": "red"}}}` is matched by
+```
+product.attributes.color:red
+```
+
+If the keys of your object contain dots, the above syntax has some ambiguity : by default `{"k8s.component.name": "quickwit"}` will be matched by 
+```k8s.component.name:quickwit```
+
+It is possible to remove the ambiguity by setting expand_dots in the json field configuration. 
+In that case, it will be necessary to escape the `.` in the query to match this document like this :
+```
+k8s\.component\.name:quickwit
+```
+
+### Clauses Cheat Sheet
+
+Quickwit support various types of clauses to express different kinds of conditions. Here's a quick overview of them:
+
+| type | syntax | examples | description| `default_search_field`|
+|-------------|--------|----------|------------|-----------------------|
+| term | `field: token` | `app_name: tantivy` <br/> `process_id:1234` <br/> `word` | A term clause tests the existence of avalue in the field's tokens | yes |
+| term prefix | `field: prefix*` | `app_name: tant*` <br/> `quick*` | A term clause tests the existence of a token starting with the provided value | yes |
+| term set | `field: IN [token token ..]` |`severity: IN [error warn]` | A term set clause tests the existence of any of the provided value in the field's tokens| yes |
+| phrase | `field: "sequence of tokens"` | `full_name: "john doe"` | A phrase clause tests the existence of the provided sequence of tokens | yes |
+| phrase prefix | `field: "sequence of tokens"*` | `title: "how to m"*` | A phrase prefix clause tests the exsitence of a sequence of tokens, the last one used like in a prefix clause | yes |
+| all | `*` | `*` | A match-all clause will match every document | no |
+| exist | `field: *` | `error: *` | An exist clause tests the existence of any value for the field, it will match only if the field exists | no |
+| range | `field: bounds` |`duration: [0 1000}` <br/> `last_name: [banner miller]` | A term clause tests the existence of a token between the provided bounds | no |
+
+## Queries
+
+Clauses can be combined using operators to form more complex queries.
+
+### Combining queries
+
+Clauses can be combined using boolean operators `AND` and  `OR` to create search exp
+An `AND` query will match only if conditions on both sides of the operator are met
+```
+type:rose AND color:red
+```
+
+An `OR` query will match if either or both conditions on each side of the operator are met
+```
+weekday:6 OR weekday:7
+```
+
+If no operator is provided, `AND` is implicitly assumed.
+
+```
+type:violet color:blue
+```
+
+### Grouping queries
+You can build complex expressions by grouping clauses using parentheses.
+```
+(type:rose AND color:red) OR (type:violet AND color:blue)
+```
+
+When no parentheses are used, `AND` takes precedence over `OR`, meaning that the following query is equivalent to the one above.
+
+```
+type:rose AND color:red OR type:violet AND color:blue
+```
+
+### Negating queries
+
+An expression can be negated either with the operator `NOT` or by prefixing the query with a dash `-`.
+
+`NOT` and `-` take precedence over everything, such that `-a AND b` means `(-a) AND b`, not `-(a AND B)`.
+
+```
+NOT severity:debug
+```
+
+or
+
+```
+type:proposal -(status:rejected OR status:pending)
+```
+
+
+## Dive deeper
+
+If you want to know more about the query language, head to the [Query Language Reference](/docs/reference/query-language-reference)