Adding NativeBase v3 template to official templates list

[makkarMeenu]

I followed these instructions to add the default template to the official template list.

I have written all the necessary changes in code as mentioned in https://github.com/codesandbox/codesandbox-client/blob/master/contributor-docs/adding-template.md , but I am unable to test it in my local if it works fine for my template.

It mentions to uncomment a particular line and change 'custom' to my templateName but I am unable to find that line in the whole project.