Update README.md

[Jake-Shadle]

Encountered an issue with pacman while going through the guide for installing the mingw toolchain on Windows with msys2, after some googling I found the solution.

I thought it would be good to update the README so people don't get frustrated. 😃

r? @steveklabnik

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @steveklabnik (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. The way Github handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[steveklabnik]

Hey @Jake-Shadle ! While this might be helpful, I'm also not sure we want to be including Pacman help in our README.

@brson has kind of been the "Guardian of the README" lately. Brian, what do you think?

[Jake-Shadle]

Cluttering the README might be bad, but as far as I can tell, any Windows user who tried the current README would fail on that step, which isn't a great user experience. Maybe just a link to the issue mentioned in this PR would suffice? eg.

_Note:_ If you have problems installing the toolchain, see here

[brson]

@Jake-Shadle what would you think of simply adding the update command as the first step, so assume they are going to have the correct packages and not run into this error? Like

# Update package list
$ pacman -Sy && pacman -S pacman-mirrors

# Choose one based on platform:
$ pacman -S mingw-w64-i686-toolchain
$ pacman -S mingw-w64-x86_64-toolchain

$ pacman -S base-devel

[jonas-schievink]

@brson I think you can just do pacman -Sy pacman-mirrors

[Jake-Shadle]

@brson took your suggestion and added the commands with a comment in the existing code block, nice and succinct!

[brson]

@Jake-Shadle What do you think of @jonas-schievink's suggestion to just write pacman -Sy pacman-mirrors?

[Jake-Shadle]

@brson Heh, fair enough, it is the main readme of the language, how is it now?

[steveklabnik]

@bors: r+ rollup

[bors]

📌 Commit 7ab8ed8 has been approved by steveklabnik

[bors]

⌛ Testing commit 7ab8ed8 with merge d3b367e...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt