git-check-attr(1): add output and example sections

Plumbing tools should document what output can be expected.

Signed-off-by: Jonas Fonseca <fonseca@diku.dk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-check-attr.txt

@@ -22,6 +22,56 @@ OPTIONS
 	arguments as path names. If not supplied, only the first argument will
 	be treated as an attribute.
 
+OUTPUT
+------
+
+The output is of the form:
+<path> COLON SP <attribute> COLON SP <info> LF
+
+Where <path> is the path of a file being queried, <attribute> is an attribute
+being queried and <info> can be either:
+
+'unspecified';; when the attribute is not defined for the path.
+'unset';;	when the attribute is defined to false.
+'set';;		when the attribute is defined to true.
+<value>;;	when a value has been assigned to the attribute.
+
+EXAMPLES
+--------
+
+In the examples, the following '.gitattributes' file is used:
+---------------
+*.java diff=java -crlf myAttr
+NoMyAttr.java !myAttr
+README caveat=unspecified
+---------------
+
+* Listing a single attribute:
+---------------
+$ git check-attr diff org/example/MyClass.java
+org/example/MyClass.java: diff: java
+---------------
+
+* Listing multiple attributes for a file:
+---------------
+$ git check-attr crlf diff myAttr -- org/example/MyClass.java
+org/example/MyClass.java: crlf: unset
+org/example/MyClass.java: diff: java
+org/example/MyClass.java: myAttr: set
+---------------
+
+* Listing attribute for multiple files:
+---------------
+$ git check-attr myAttr -- org/example/MyClass.java org/example/NoMyAttr.java
+org/example/MyClass.java: myAttr: set
+org/example/NoMyAttr.java: myAttr: unspecified
+---------------
+
+* Not all values are equally unambiguous:
+---------------
+$ git check-attr caveat README
+README: caveat: unspecified
+---------------
 
 SEE ALSO
 --------