Update api.md to reflect documentation support for 5x10 displays

[buddywhitman]

Found this issue in the arduino/Arduino repository where a user had trouble finding the documentation for her unique 1-line 5x10 char LCD display in the LiquidCrystal references page since she could not satisfactorily display the extended 32 characters due to the default charsize value in:

void begin(uint8_t cols, uint8_t rows, uint8_t charsize = LCD_5x8DOTS);

They had to manually dig into the source code to find this method and define the extended 5x10 font support.

This commit should help users with similar boards get started easily with the LiquidCrystal library using the overloaded begin() invocation with relevant docs available on the website, without any need to painstakingly go through the source code.

[CLAassistant]

All committers have signed the CLA.

[buddywhitman]

@per1234 I have implemented the requested changes in the latest commit.

[buddywhitman]

Thanks so much for your contribution @buddywhitman!

This was my first open source contribution haha.