Fix found problems in the doc after review

Author: Vitaly Davydov

README.pg_sphere

@@ -11,7 +11,7 @@ It provides:
 
 This is an R-Tree implementation using GiST for spherical objects like
 spherical points and spherical circles with useful functions and operators.
-It also support the Block Range INdexing (BRIN) for large datasets.
+It also supports the Block Range INdexing (BRIN) for large datasets.
 
 NOTICE:
      This version will work only with PostgreSQL version 10 and above.

doc/indices.sgm

@@ -15,7 +15,7 @@
           of data blocks (<literal>pages</literal>) on physical storage in order to
           organize data searches on ranges of summarized data that can be easily skipped
           on the base of search filters (see <ulink
-          url="https://www.postgresql.org/docs/9.5/static/brin-intro.html"><citetitle>
+          url="https://www.postgresql.org/docs/current/brin-intro.html"><citetitle>
           PostgreSQL documentation</citetitle></ulink> for further details on BRINs).
           As a consequence, BRINs result to be really small indexes (up to 1000 times
           than GiST ones), generally with lower a performance compared with a GiST one,
@@ -90,11 +90,12 @@
 <![CDATA[CREATE INDEX test_pos_idx USING BRIN ON test (pos);]]>
           </programlisting>
           <para>
-            By default, BRINs summarize block of 128 pages. The lower numbers
-            of pages are specified, the higher granularity is reached during
-            the searches, and performance's gap between GiST indexes and BRINs
-            is lower (consider that BRINs size increases as well). Different
-            summarizations can be used with the following command:
+            By default, BRINs summarize blocks of 128 pages. The smaller the
+            number of pages specified, the higher the granularity in searches,
+            and the gap in performance between GiST indexes and BRINs will be
+            decreased. Note that the size of the BRINs increases as well.
+            Different summarizations can be specified with the following
+            command:
           </para>
           <programlisting>
 <![CDATA[CREATE INDEX test_pos_idx USING BRIN ON test (pos) WITH (pages_per_range = 16);]]>