docs: Clarify --with-segsize-blocks documentation

Without the added "relation" it's not immediately clear that the option
relates to the relation segment size and not e.g. the WAL segment size.

The option was added in d3b111e32.

Reported-by: Tom Lane 
Discussion: https://postgr.es/m/837536.1695348498@sss.pgh.pa.us
Backpatch: 16-

diff --git a/doc/src/sgml/installation.sgml b/doc/src/sgml/installation.sgml
index 75dc81a0a9e25c6f5a50a7caaf9b7191c309fa12..37f542a325e2e89635f5283731dba3c63ba820e4 100644 (file)
--- a/doc/src/sgml/installation.sgml
+++ b/doc/src/sgml/installation.sgml
@@ -1694,7 +1694,7 @@ build-postgresql:
        --with-segsize-blocks=SEGSIZE_BLOCKS
        
         
-         Specify the segment size in blocks. If both
+         Specify the relation segment size in blocks. If both
          --with-segsize and this option are specified, this
          option wins.
 
@@ -3191,7 +3191,7 @@ ninja install
        -Dsegsize_blocks=SEGSIZE_BLOCKS
        
         
-         Specify the segment size in blocks. If both
+         Specify the relation segment size in blocks. If both
          -Dsegsize and this option are specified, this option
          wins.