"Install" is not a noun, and while it might be acceptable to use the verb as a noun, it is not correct. Using the correct
noun, "installation", increases clarity, especially for non-native English speakers.
This change fixes the usage in user-facing text and in developer documentation.
Fixes#41620
git-svn-id: https://develop.svn.wordpress.org/trunk@41289 602fd350-edb4-49c9-b593-d223f7449a82