add more states to tax section (#5466)

Adds missing states where sales tax is collected

Author: imatwawana

src/docs/product/accounts/pricing.mdx

@@ -160,11 +160,14 @@ As of December 1, 2020, customers with a US-based billing address may be subject
 
 - Connecticut
 - District of Columbia
+- Maryland
 - Massachusetts
 - New Mexico
 - New York
 - Ohio
 - Pennsylvania
+- Rhode Island
+- South Carolina
 - Texas
 - Utah
 - Washington