update search docs (#92)

docs/user/search.md

@@ -11,10 +11,9 @@ inspecting their content, title, and tags.
 	{{extra.project}} searches only in **content of the last version** of the document
 
 
-By default, {{extra.project}} returns only documents which contain all words typed in
-the search bar. However, {{extra.project}} also offers additional search syntax if you
-want to drill down the results further.
-
+By default, {{extra.project}} returns only documents which contain any of the
+words typed in the search bar. However, {{extra.project}} also offers
+additional search syntax if you want to drill down the results further.
 
 Matching inexact words:
 
@@ -27,3 +26,33 @@ Matching specific tags:
 	tags:paid
 
 will return documents with tag "paid"
+
+
+You can match document with logical expressions:
+
+	pizza AND salami
+
+will return all documents containing both words: "pizza" and "salami".
+
+	pizza AND (salami OR speciale)
+
+will return all documents containing either "pizza" and "salami";
+or "pizza" and "speciale".
+
+!!! note
+
+	Logical expression must be in capital case, otherwise they
+	will be ignored.
+
+Implicit logical expression is "OR". In other words, if you search:
+
+	pizza salami
+
+is same as you would search with following query:
+
+	pizza OR salami
+
+All of these constructs can be combined as you see fit.
+For example, following search query will return all documents tagged with "important" and contain word "pizza":
+
+	pizza AND tags:important