Alter phrasing to clarify where info is stored.

A user on #matrix:matrix.org was confused by the phrasing of the first
sentence in the paragraph and couldn't tell whether it was saying that
the homeserver stored the data or the clients did. This change splits it
into two sentences to make the subject of each sentence clear.

README.rst

@@ -58,12 +58,13 @@ the spec in the context of a codebase and let you run your own homeserver and
 generally help bootstrap the ecosystem.
 
 In Matrix, every user runs one or more Matrix clients, which connect through to
-a Matrix homeserver which stores all their personal chat history and user
-account information - much as a mail client connects through to an IMAP/SMTP
-server. Just like email, you can either run your own Matrix homeserver and
-control and own your own communications and history or use one hosted by
-someone else (e.g. matrix.org) - there is no single point of control or
-mandatory service provider in Matrix, unlike WhatsApp, Facebook, Hangouts, etc.
+a Matrix homeserver. The homeserver stores all their personal chat history and
+user account information - much as a mail client connects through to an
+IMAP/SMTP server. Just like email, you can either run your own Matrix
+homeserver and control and own your own communications and history or use one
+hosted by someone else (e.g. matrix.org) - there is no single point of control
+or mandatory service provider in Matrix, unlike WhatsApp, Facebook, Hangouts,
+etc.
 
 Synapse ships with two basic demo Matrix clients: webclient (a basic group chat
 web client demo implemented in AngularJS) and cmdclient (a basic Python