[apm docs consolidation] 8.10: Delete moved files, update README (#12356)

* delete files, update README

* update README

Author: colleenmcginnis

README.md

@@ -11,7 +11,7 @@ For questions and feature requests, visit the [discussion forum](https://discuss
 
 ## Getting Started
 
-To get started with APM, see our [Quick start guide](https://www.elastic.co/guide/en/apm/get-started/current/install-and-run.html).
+To get started with APM, see our [Quick start guide](https://www.elastic.co/guide/en/apm/guide/current/apm-quick-start.html).
 
 ## APM Server Development
 
@@ -154,5 +154,13 @@ Building pre-release images can be done by running `make package-docker-snapshot
 
 ## Documentation
 
-[Documentation](https://www.elastic.co/guide/en/apm/server/current/index.html)
-for the APM Server can be found in the `docs` and `dev_docs` folders.
+Documentation for the APM Server can be found in the [APM guide](https://www.elastic.co/guide/en/apm/guide/8.10/index.html). Most documentation files live in the [elastic/observability-docs](https://github.com/elastic/observability-docs) repo's [`docs/en/apm-server/` directory](https://github.com/elastic/observability-docs/tree/8.10/docs/en/apm-server).
+
+However, the following content lives in this repo:
+
+* The **changelog** page listing all release notes is in [`CHANGELOG.asciidoc`](/CHANGELOG.asciidoc).
+* Each minor version's **release notes** are documented in individual files in the [`changelogs/`](/changelogs/) directory.
+* A list of all **breaking changes** are documented in [`changelogs/all-breaking-changes.asciidoc`](/changelogs/all-breaking-changes.asciidoc).
+* **Sample data sets** that are injected into the docs are in the [`docs/data/`](/docs/data/) directory.
+* **Specifications** that are injected into the docs are in the [`docs/spec/`](/docs/spec/) directory.
+

dev_docs/RELEASES.md

@@ -9,7 +9,7 @@ For patch releases, only the version on the existing major and minor version bra
 
 ## Feature Freeze
 
-* For patch releases, ensure all relevant backport PRs are merged. 
+* For patch releases, ensure all relevant backport PRs are merged.
   We use backport labels on PRs and automation to ensure labels are set.
 
 * Update Changelog
@@ -30,9 +30,9 @@ For patch releases, only the version on the existing major and minor version bra
     Update versions and ensure that the `BEATS_VERSION` in the Makefile is updated,
     e.g. [#2803](https://github.com/elastic/apm-server/pull/2803/files).
     Trigger a new beats update, once the beats branch is also created.
-    Remove the [changelogs/head.asciidoc](https://github.com/elastic/apm-server/blob/main/changelogs/head.asciidoc) file from the release branch. 
+    Remove the [changelogs/head.asciidoc](https://github.com/elastic/apm-server/blob/main/changelogs/head.asciidoc) file from the release branch.
 
-  * Main branch: 
+  * Main branch:
     Update [.mergify.yml](https://github.com/elastic/apm-server/blob/main/.mergify.yml) with a new backport rule for the next version,
     and update versions to next minor version, e.g. [#2804](https://github.com/elastic/apm-server/pull/2804).
 
@@ -86,7 +86,7 @@ For patch releases, only the version on the existing major and minor version bra
 
 ## When compatibility between Agents & Server changes
 
-* Update the [agent/server compatibility matrix](https://github.com/elastic/apm-server/blob/main/docs/guide/agent-server-compatibility.asciidoc).
+* Update the [agent/server compatibility matrix](https://github.com/elastic/observability-docs/blob/main/docs/en/observability/apm/agent-server-compatibility.asciidoc) in the elastic/observability repo.
 
 ## Templates