doc: Fix some grammar

This is an extraction of the user-visible changes done in 410aa24,
including all the relevant documentation parts.

Author: Justin Pryzby
Discussion: https://postgr.es/m/20220124030001.GQ23027@telsasoft.com
Backpatch-through: 10

doc/src/sgml/protocol.sgml

@@ -1975,7 +1975,7 @@ The commands accepted in replication mode are:
       streaming starts on timeline <replaceable class="parameter">tli</replaceable>;
       otherwise, the server's current timeline is selected. The server can
       reply with an error, for example if the requested section of WAL has already
-      been recycled. On success, server responds with a CopyBothResponse
+      been recycled. On success, the server responds with a CopyBothResponse
       message, and then starts to stream WAL to the frontend.
      </para>
 

doc/src/sgml/ref/pg_receivewal.sgml

@@ -83,9 +83,8 @@ PostgreSQL documentation
     <listitem>
      <para>
       First, scan the directory where the WAL segment files are written and
-      find the newest completed segment file, using as starting point the
-      beginning of the next WAL segment file. This is calculated independently
-      on the compression method used to compress each segment.
+      find the newest completed segment file, using as the starting point the
+      beginning of the next WAL segment file.
      </para>
     </listitem>
 
@@ -93,7 +92,7 @@ PostgreSQL documentation
      <para>
       If a starting point cannot be calculated with the previous method,
       the latest WAL flush location is used as reported by the server from
-      a <literal>IDENTIFY_SYSTEM</literal> command.
+      an <literal>IDENTIFY_SYSTEM</literal> command.
      </para>
     </listitem>
    </orderedlist>