Modify ReadMe.md to address default character set issue with windows

When creating databases and tables with mysql/mariadb on Windows servers, the default character set is UTF8MB3. The character set UTF8MB3 allows for columns to store up to 3 bytes.

The display_symbol column in the fineract_default.m_currency table requires 4bytes, so if the default character set is used when creating the database fineract_default with the following command:

CREATE DATABASE fineract_default

then the migration script to insert the currencies will fail with an error similar to:

Incorrect string value: `\xE2\x82\xA1` for column display_symbol ...

To rectify this, the default character set has to be overridden when creating the fineract_default database with the following command

CREATE DATABASE fineract_default CHARACTER SET utf8mb4

This allows for the 4bytes needed to store the data in the m_currency.display_symbol and the migration script will run just fine.