README: give pkg its own quickstart profile

Both attach lines pointed at MEM_SHM, whose 1024 MB scale-up target is
shared-arena scale - per-worker pkg wants numbers an order of magnitude
smaller. The quickstart now shows a separate MEM_PKG profile.

Author: Lt-Flash

README.md

@@ -133,11 +133,17 @@ auto_scaling_profile = MEM_SHM
     scale up to 1024 on 80% for 3 cycles within 10
     scale down to 256 on 30% for 120 cycles
 
+auto_scaling_profile = MEM_PKG
+    scale up to 64 on 80% for 2 cycles within 5
+    scale down to 8 on 20% for 60 cycles
+
 shm_auto_scaling_profile = MEM_SHM
+pkg_auto_scaling_profile = MEM_PKG
 ```
 
-`pkg_auto_scaling_profile` takes the same grammar and does the same
-for every worker's private arena — Section 11.
+The pkg profile governs **every worker's private arena individually**,
+so its numbers are per-worker scale — an order of magnitude below the
+shared arena's (Section 11).
 
 Watch it work:
 

mem/README.hg_malloc_v3.md

@@ -127,11 +127,17 @@ auto_scaling_profile = MEM_SHM
     scale up to 1024 on 80% for 3 cycles within 10
     scale down to 256 on 30% for 120 cycles
 
+auto_scaling_profile = MEM_PKG
+    scale up to 64 on 80% for 2 cycles within 5
+    scale down to 8 on 20% for 60 cycles
+
 shm_auto_scaling_profile = MEM_SHM
+pkg_auto_scaling_profile = MEM_PKG
 ```
 
-`pkg_auto_scaling_profile` takes the same grammar and does the same
-for every worker's private arena — Section 11.
+The pkg profile governs **every worker's private arena individually**,
+so its numbers are per-worker scale — an order of magnitude below the
+shared arena's (Section 11).
 
 Watch it work: