bootstrap-haskell: s/will download/can download/

A one word tweak to weaken the language in the initial explanation to make it "less scary": in general ghcup does not always download all of ghcup, ghc, cabal, stack, and hls (unless requested or they are not already installed, etc), but "will download" sounds like the user has no choice here except to always download everything, which might give them second thoughts about trying this script and hence adopting ghcup.

Perhaps the wording could be made further more precise, but at least "can" gives one less anxiety.

scripts/bootstrap/bootstrap-haskell

@@ -688,7 +688,7 @@ find_shell
 echo
 echo "Welcome to Haskell!"
 echo
-echo "This script will download and install the following binaries:"
+echo "This script can download and install the following binaries:"
 echo "  * ghcup - The Haskell toolchain installer"
 echo "  * ghc   - The Glasgow Haskell Compiler"
 echo "  * cabal - The Cabal build tool for managing Haskell software"