Update README.md (trustwallet#5449)

README.md

@@ -29,7 +29,7 @@ Here is a quick starter summary for the most common use case.
 - [ ] Make sure your smartcontract has more than 2,500 address holders, otherwise you will be rejected
 - [ ] Fork the Github repository
 - [ ] Create folder with name of token smartcontact address in [_checksum format_](https://developer.trustwallet.com/add_new_asset#checksum_format) `blockchains/ethereum/assets/<token_smartcontract_address>/`.
-- [ ] Tell your designer that token image must be in PNG format, recommended size 256x256px, max. 512x512px, with max file size of 100kB, for further details read [image rules](https://developer.trustwallet.com/add_new_asset#image-requirements).
+- [ ] Tell your designer that token image must be in PNG format, avoid transparent background, recommended size 256x256px, max. 512x512px, with max file size of 100kB, for further details read [image rules](https://developer.trustwallet.com/add_new_asset#image-requirements).
 - [ ] Upload your logo with file named `logo.png` to previously created folder with smartcontract address, and if you done all correctly your path should look like this. `blockchains/ethereum/assets/0x1234567461d3f8Db7496581774Bd869C83D51c93/logo.png`
 - [ ] Create a pull request to the main repo
 - [ ] Pay the processing fee