doc: document prepublish-on-install deprecation

Now all we have to remember to do is come back to this when we put out
`npm@5`.

PR-URL: npm/npm#14290
Credit: @othiym23
Reviewed-By: @watilde
Reviewed-By: @iarna
Reviewed-By: @zkat

doc/misc/npm-scripts.md

@@ -6,9 +6,14 @@ npm-scripts(7) -- How npm handles the "scripts" field
 npm supports the "scripts" property of the package.json script, for the
 following scripts:
 
+* prepare:
+  Run both before the package is published, and on local `npm
+  install` without any arguments. (See below.)
 * prepublish:
   Run BEFORE the package is published.  (Also run on local `npm
-  install` without any arguments.)
+  install` without any arguments. See below.)
+* prepublishOnly:
+  Run BEFORE the package is published. (See below.)
 * publish, postpublish:
   Run AFTER the package is published.
 * preinstall:
@@ -43,7 +48,30 @@ names will be run for those as well (e.g. `premyscript`, `myscript`,
 `postmyscript`). Scripts from dependencies can be run with `npm explore
 <pkg> -- npm run <stage>`.
 
-## COMMON USES
+## PREPUBLISH AND PREPARE
+
+### DEPRECATION NOTE
+
+Since `[email protected]`, the npm CLI has run the `prepublish` script for both `npm
+publish` and `npm install`, because it's a convenient way to prepare a package
+for use (some common use cases are described in the section below).  It has
+also turned out to be, in practice, [very
+confusing](https://github.com/npm/npm/issues/10074).  As of `[email protected]`, a new
+event has been introduced, `prepare`, that preserves this existing behavior. A
+_new_ event, `prepublishOnly` has been added as a transitional strategy to
+allow users to avoid the confusing behavior of existing npm versions and only
+run on `npm publish` (for instance, running the tests one last time to ensure
+they're in good shape).
+
+**IMPORTANT:** As of `npm@5`, `prepublish` will _only_ be run for `npm
+publish`.  This will make its behavior identical to `prepublishOnly`, so
+`npm@6` or later may drop support for the use of `prepublishOnly`, and then
+maybe we can all forget this embarrassing thing ever happened.
+
+See <https://github.com/npm/npm/issues/10074> for a much lengthier
+justification, with further reading, for this change.
+
+### USE CASES
 
 If you need to perform operations on your package before it is used, in a way
 that is not dependent on the operating system or architecture of the