Update 01-what-is-git.md

[infoglut]

Fixed a typo - exampleV3.text should be exampleV3.txt for consistency Added "and spreadsheets" to the examples of file types that GitHub can work with. Updated language - replaced constantly with regularly in this sentence "constantly updated text books" - the use of constantly doesn't make sense in the usage.

Instructions

Thanks for contributing! :heart: If this contribution is for instructor training, please email the link to this contribution to checkout@carpentries.org so we can record your progress. You've completed your contribution step for instructor checkout by submitting this contribution! Keep in mind that **lesson maintainers are volunteers** and it may take them some time to respond to your contribution. Although not all contributions can be incorporated into the lesson materials, we appreciate your time and effort to improve the curriculum. If you have any questions about the lesson maintenance process or would like to volunteer your time as a contribution reviewer, please contact The Carpentries Team at team@carpentries.org. You may delete these instructions from your comment. \- The Carpentries

[dcmcand]

Hi @infoglut , Thanks so much for your contribution. We appreciate you helping to make the Carpentries lessons better. I have merged your change.