Fix typo in "Installing"

[kayleachampion]

In the bulleted list under "Full installation details..." in the "Prerequisites" section of the INSTALL.md file, the word "Intallling" should be corrected to be "Installing".

[AB-programmer8]

I would like to work on this please!

[github-actions]

Great! I assigned you (@AB-programmer8) to the issue. Have fun working on it!