Adds the rfc for removing yarn check

Author: Maël Nison

accepted/0000-remove-yarn-check.md

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+- Start Date: 30 Oct 2018
+- RFC PR: https://github.com/yarnpkg/rfcs/pull/106
+- Yarn Issue: n/a
+
+# Remove `yarn check`
+
+## 1. Motivation
+
+Running `yarn install` should work out of the box. There's no reason for `yarn check` to exist from a user perspective - they should never have to run it, because installs must always be right.
+
+Being not particularly useful, the `yarn check` command receives less attention and as a result it often yields wrong / confusing results. This leads users to believe that `yarn install` is broken when it's in fact `yarn check` (https://twitter.com/betaorbust/status/1055610508533878784).
+
+## 2. Detailed Design
+
+We'll remove the `yarn check` command in Yarn 2.0.
+
+## 3. How Can We Teach This
+
+This command will be marked as deprecated, and running it will exit with an error code and an error message explaining why it got removed.
+
+## 4. Drawbacks
+
+- The one use of `yarn check` is to provide debug information when installs aren't properly made. In practice it's never used this way, even by maintainers.
+
+## 5. Alternatives
+
+- We could fix `yarn check`. This would prove time consuming, of little value because of the reasons detailed above, and resources would be better spent on other worksites.