chore: add release plan [skip ci]

RELEASE_PLAN.md

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+## Release Plan
+
+Starting with version `v2.4`, the Nuxt core team will adhere to a formalized release plan (as good as possible).
+Also, an end of life for older major versions is defined with this document
+
+### Major versions (3.x.y, 4.x.y, ...)
+
+We aim for a major release once every **6 months**. This depends on a few factors though:
+
+* Major version releases of critical dependencies like Vue, Webpack or Babel
+* Number of breaking changes "in the queue"
+
+Our goal is to provide a **migration guide** for each major version as well as escape hatches so existing code
+won't "just break".
+
+### Minor versions
+
+The team agree on a release cycle of (roughly) **4 weeks**. 
+
+Three of the for weeks will be used for actual **feature implementations** while the last week will be used for 
+**testing, fixing bugs and thorough audits**.
+
+That also means a *feature freeze* for the next minor version after these three weeks.
+Features that aren't ready will be moved to the next cycle. We try to avoid to "wait" for features 
+(for a longer time) to keep releases lean, concise, predictable and digestible.
+
+### Patch releases
+
+The last patch releases were mostly *bundled* fixes or single *hotfixes*. 
+In the future we will avoid this practice and try to release each fix **as soon as possible** after the actual PR/commit.
+People won't have to switch to `nuxt-edge` for bugfixes then.
+
+Fixes can or will include:
+
+* Updates of dependencies (for various reasons, like a "faulty/buggy" dependency or an newer versions that works better with the Nuxt.js code)
+* Fixes for our code
+
+Bugfixes for upcoming features won't be ported of course.
+
+### Edge releases
+
+We've experimented with `nuxt-edge` releases in the last time and decided to do **nightly releases** for now instead of 
+releasing a version after *each commit*.
+
+## End Of Life
+
+We agreed to set an **End Of Life** for older major Nuxt.js versions. 
+Previous releases will receive security updates and bugfixes *until two weeks after the second next major release*. 
+As we release new majors approximately once every 6 months, this will allow people to "skip one major version" without
+being stuck with a buggy or unsecure Nuxt.js dependency.
+There will be a detailed migration guide for each major update.
+The EOL also applies to the documentation.
+
+### Example
+We are on Nuxt 2 right now. When Nuxt three would be released tomorrow, Nuxt 2 would still receive fixes. 
+Imagine nuxt 4 would release exactly 1 week after (which is unlikely but for the sake of the example). 
+Then the countdown for the End Of Life for Nuxt 2 would start. 
+Two weeks after the Nuxt 4 release, we will stop maintaining Nuxt 2.