Re: minor doc work

Neil Conway wrote:
>       If <command>SET</> is allowed, it overrides all other sources of
> !     values for the parameter.  Superusers are allowed to
> !     <command>SET</> more values than ordinary users.  Some parameters
> !     cannot be <command>SET</command> even by superusers: for example,

Please don't use marked up command names as verbs.  Next week you'll be
<command>UPDATE</command>ing or something.  Here, there is no chance for
confusion, so just write "cannot be set" or "cannot be changed with
<command>SET</command>".  In fact, the latter is even clearer.

> !     if they control behavior that cannot reasonably be changed without
> !     restarting <productname>PostgreSQL</productname>.