Merge pull request MaterializeInc#1810 from rjnn/docs3

doc: edit landing page text

doc/user/_index.md

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-Materialize is a streaming SQL materialized view engine.
+Materialize is a streaming data warehouse. Materialize accepts input data from a
+variety of streaming sources (such as Kafka), and queries in the PostgreSQL
+dialect of SQL.
 
 ## What does Materialize do?
 
 Materialize lets you ask questions about your data, and then get the answers in
 real time.
 
 Why not just use your database's built-in functionality to perform these same
-computations? Because your database acts as if it's never been asked that
+computations? Because your database often acts as if it's never been asked that
 question before, which means it can take a _long_ time to come up with an
 answer, each and every time you pose the query.
 
 Materialize instead keeps the results of the queries and incrementally updates
-them as new data comes in. So, rather than recalculating the answer each time it's
-asked, Materialize continually updates the answer and gives you the answer's
-current state from memory.
+them as new data comes in. So, rather than recalculating the answer each time
+it's asked, Materialize continually updates the answer and gives you the
+answer's current state from memory.
+
+Importantly, Materialize supports incrementally updating a much broader set of
+views than is common in traditional databases (e.g. views over multi-way joins
+with complex aggregations), and can do incremental updates in the presence of
+arbitrary inserts, updates, and deletes in the input streams.
 
 ## Why should I use Materialize?
 
 If you perform any OLAP queries over relational data and want to reduce the time
 it takes to refresh answers to common queries, Materialize can make that happen.
 
 For a sense of scale, it can take queries that most teams would run once-per-day
-and instead provide real-time answers.
+and instead provide sub-second or single-digit second answers.
 
 ## Learn more