primary key display in psql

When you look at a table definition with psql \d, one of the arguably
most important pieces of information -- the primary key -- is hidden
somewhere below under "indexes":
   Table "public.test2"Column |  Type   | Modifiers
--------+---------+-----------a      | integer | not nullb      | integer | not null
Indexes:   "test2_pkey" PRIMARY KEY, btree (a, b)

I think we could easily improve that by having it look something like
this instead:
   Table "public.test2"Column |  Type   | Modifiers
--------+---------+-----------a      | integer | PKb      | integer | PK
Indexes:   "test2_pkey" PRIMARY KEY, btree (a, b)

Since there can only be one primary key, this should be unambiguous.

I don't have time to code this up right now, but maybe someone feels
inspired.  What do you think?