Add BatteryMHM preprint (PAPER.md + PDF); link from model card

.gitattributes

@@ -33,3 +33,4 @@ saved_model/**/* filter=lfs diff=lfs merge=lfs -text
 *.zip filter=lfs diff=lfs merge=lfs -text
 *.zst filter=lfs diff=lfs merge=lfs -text
 *tfevents* filter=lfs diff=lfs merge=lfs -text
+docs/BatteryMHM_paper.pdf filter=lfs diff=lfs merge=lfs -text

docs/BatteryMHM_paper.pdf

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:37c8e32469675514db0a1b850b654621a06b8ed0f277b5441d08d293cbe4897f
+size 253101