Clarify prose about querier frontend min-sharding-lookback (#4050)

* Clarify prose about querier frontend min-sharding-lookback

Docs edit of prose from #4047.

* Update docs/sources/configuration/_index.md

Co-authored-by: Danny Kopping <dannykopping@gmail.com>

Co-authored-by: Owen Diehl <ow.diehl@gmail.com>
Co-authored-by: Danny Kopping <dannykopping@gmail.com>

docs/sources/configuration/_index.md

@@ -322,8 +322,9 @@ The queryrange_config configures the query splitting and caching in the Loki que
 [split_queries_by_interval: <duration> | default = 0s]
 
 # Limit queries that can be sharded.
-# Queries with time range that fall between now and now minus the sharding lookback are not sharded.
-# Default value is 0s (disable), meaning all queries of all time range are sharded.
+# Queries within the time range of now and now minus this sharding lookback
+# are not sharded. The default value of 0s disables the lookback, causing
+# sharding of all queries at all times.
 # CLI flag: -frontend.min-sharding-lookback
 [min_sharding_lookback: <duration> | default = 0s]