Clarify that {a="b",a!="c"} is possible. (#4492)

Signed-off-by: Brian Brazil <brian.brazil@robustperception.io>

docs/querying/basics.md

@@ -95,8 +95,9 @@ For example, this selects all `http_requests_total` time series for `staging`,
 
     http_requests_total{environment=~"staging|testing|development",method!="GET"}
 
-Label matchers that match empty label values also select all time series that do
-not have the specific label set at all. Regex-matches are fully anchored.
+Label matchers that match empty label values also select all time series that
+do not have the specific label set at all. Regex-matches are fully anchored. It
+is possible to have multiple matchers for the same label name.
 
 Vector selectors must either specify a name or at least one label matcher
 that does not match the empty string. The following expression is illegal: