pgsql: doc: Copy-edit the "Overview of PostgreSQL Internals" chapter

doc: Copy-edit the "Overview of PostgreSQL Internals" chapter

Rephrase a few sentences to be more concise.

Refer to the postmaster process as "postmaster", not "postgres". This
originally said "postmaster process", but was changed to "postgres
process" in commit 5266f221a2, when we merged the "postmaster" and
"postgres" commands, and "postmaster" became just a symlink. That was a
case of overzealous search & replace, because the process is still called
"postmaster".

Author: Erik Rijkers and Jürgen Purtz
Discussion: https://www.postgresql.org/message-id/aa31f359-1168-ded5-53d0-0ed228bfe097%40iki.fi

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/29ad6595ef7f568ca11dd9219c0d23048bdda513

Modified Files
--------------
doc/src/sgml/arch-dev.sgml | 27 ++++++++++++---------------
1 file changed, 12 insertions(+), 15 deletions(-)