Navigate to https://webapp.643charts.com/interface/

Click on any EDIT icon where ever you'd like to place the Notes Section.

Navigate to https://webapp.643charts.com/interface/custom-sprays#report-designer

You can also see in the dropdown here that you have an "EMPTY" option. This will make that area of the report blank. This is helpful if you want to pull in your own materials or data to the report after export. 

You now have a section for notes on your Custom Report!

STANDARD STATS

BA	H	BABIP	OBP	SLG	OPS
.368	200	.412	.474	.532	1.006
K	KL	BB	HBP	R	GDP
82	29	85	29	146	7
BUNTS	SAC	BNT 1B	DRAG	PUSH	SQZ
11	3	3	0	0	0
SB	SB2	SB3	PO	INF 1B	SPD
44/58	41/54	3/3	4	23	6.82

Adding a Notes Section to a Custom Report Template