docs: fix "timeseries" -> "time series" in README.md (prometheus#8107)

Signed-off-by: Piper <[email protected]>

README.md

@@ -18,11 +18,11 @@ to be true.
 
 Prometheus's main distinguishing features as compared to other monitoring systems are:
 
-- a **multi-dimensional** data model (timeseries defined by metric name and set of key/value dimensions)
+- a **multi-dimensional** data model (time series defined by metric name and set of key/value dimensions)
 - PromQL, a **powerful and flexible query language** to leverage this dimensionality
 - no dependency on distributed storage; **single server nodes are autonomous**
-- timeseries collection happens via a **pull model** over HTTP
-- **pushing timeseries** is supported via an intermediary gateway
+- time series collection happens via a **pull model** over HTTP
+- **pushing time series** is supported via an intermediary gateway
 - targets are discovered via **service discovery** or **static configuration**
 - multiple modes of **graphing and dashboarding support**
 - support for hierarchical and horizontal **federation**