add blog post about v1.13 (magefile#412)

* add blog post about v1.13

site/content/blog/release-v1.13.0.md

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+title = "Release v1.13.0 - Magefiles Directory"
+date = 2022-03-18T08:17:52-05:00
+type = "post"
+author = "Nate Finch"
+authorLink = "twitter.com/natethefinch"
++++
+
+[Mage v1.13.0](https://github.com/magefile/mage/releases/tag/v1.13.0) is now
+released with a few fixes and one big new feature - the magefiles subdirectory.
+
+You can now put your magefiles in a subdirectory of your repo called
+`/magefiles`, and Mage will find them automatically, like it always has for
+files in the root. Files in `/magefiles` do not need the `mage` build tag to be
+discovered by Mage (but if it’s there, it’ll still find them).
+
+This is a big change that will be a significant quality of life improvement for
+many developers. Until now, Mage was designed to allow you to keep magefiles in
+the root of your repo, tagged with the `mage` build tag, so that your normal go
+build tooling would ignore them. However, this had the side effect of meaning
+that linting etc would *also* ignore them. You could add the `mage` build tag to
+your IDE and/or gopls, but because Mage also requires the files to be in
+`package main`, this could result in having files from two different packages in
+the root of your repo, which would cause linters and gopls to complain.
+
+Now, you can put those files in a separate directory, and you don’t even need
+the build tag any more. No conflicting packages, no need to twiddle with build
+tags, and all this is automatic, no settings need to be adjusted, you just need
+Mage v1.13+.
+
+Migrating your magefiles from the root of your repo to a subdirectory is
+trivial. Just copy them into `/magefiles`.  That’s it. Mage will continue to
+work like it always has. If you like, you can remove the build tags, mage
+doesn’t care if they’re there or not.
+
+For backwards compatibility reasons, if you have magefiles in the root of your
+repo (defined as .go files with the `mage` build tag), and you have a `/magefiles`
+subdirectory, Mage will default to the old behavior of only looking at the files
+in the root directory. This is to avoid breaking anyone who happened to already
+have a `/magefiles` directory. In this instance, Mage v1.13 will print out a
+warning when you run it, noting that it’s using the files in the root of the
+repo. 
+
+Because this behavior requires some extra time and work even if you *don’t* have
+magefiles in the root directory, **in the future** we plan to change the default
+so that Mage looks for the `/magefiles` subdirectory first, and ignores any
+files in the root unless there is no `/magefiles` directory. We have no plans to
+drop support for using files in the root directory, but if you want to continue
+using that behavior, you'll eventually need to rename the `/magefiles`
+subdirectory (but again, that's planned for the future, not right now). 
+
+Note that as of 1.13, Mage still requires those files to be in `package main`.
+We plan to remove that requirement in the future, so that linters won’t complain
+about the missing `func main`. 
+
+We hope this helps fix most of the problems some people have had using Mage with
+standard Go tooling. Please feel free to post any questions you have in the
+`#mage` channel of [gophers slack](https://gophers.slack.com/messages/mage/), or
+on the [discussions board](https://github.com/magefile/mage/discussions) on
+Mage’s [github repo](https://github.com/magefile/mage). Happy building!