doc: pg_buffercache documentation wordsmithing

A words seemed to have gone missing in the leading paragraphs.

Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Co-authored-by: Daniel Gustafsson <daniel@yesql.se>
Discussion: https://postgr.es/m/aGTQYZz9L0bjlzVL@ip-10-97-1-34.eu-west-3.compute.internal
Backpatch-through: 18

doc/src/sgml/pgbuffercache.sgml

@@ -37,12 +37,12 @@
 
  <para>
   This module provides the <function>pg_buffercache_pages()</function>
-  function (wrapped in the <structname>pg_buffercache</structname> view),
+  function (wrapped in the <structname>pg_buffercache</structname> view), the
   <function>pg_buffercache_numa_pages()</function> function (wrapped in the
   <structname>pg_buffercache_numa</structname> view), the
   <function>pg_buffercache_summary()</function> function, the
   <function>pg_buffercache_usage_counts()</function> function, the
-  <function>pg_buffercache_evict()</function>, the
+  <function>pg_buffercache_evict()</function> function, the
   <function>pg_buffercache_evict_relation()</function> function and the
   <function>pg_buffercache_evict_all()</function> function.
  </para>
@@ -55,7 +55,7 @@
  </para>
 
  <para>
-  The <function>pg_buffercache_numa_pages()</function> provides
+  The <function>pg_buffercache_numa_pages()</function> function provides
   <acronym>NUMA</acronym> node mappings for shared buffer entries. This
   information is not part of <function>pg_buffercache_pages()</function>
   itself, as it is much slower to retrieve.