Add upgrade notes for 5.0.0-rc.1 (#112)

Signed-off-by: nscuro <nscuro@protonmail.com>

Author: nscuro

docs/guides/upgrading/.pages

@@ -1,6 +1,7 @@
 title: Upgrade guides
 nav:
   - index.md
+  - v5.0.0-rc.1.md
   - v0.7.0-alpha.9.md
   - v0.7.0-alpha.8.md
   - v0.7.0-alpha.7.md

docs/guides/upgrading/v5.0.0-rc.1.md

@@ -0,0 +1,23 @@
+# Upgrading to v5.0.0-rc.1
+
+!!! tip
+    Version `5.0.0-rc.1` is effectively the same as [`0.7.0-alpha.9`](v0.7.0-alpha.9.md).
+    No manual upgrade steps or database migrations are necessary other than updating container
+    image names and tags as outlined below.
+
+* **Updated versioning**. The Hyades project moves back to mainline Dependency-Track. The versioning now accurately
+  reflects it being the next major version of Dependency-Track. What was "Hyades `0.7.0-alpha.9`",
+  "Hyades API server `5.7.0-alpha.9`", and "Hyades frontend `5.7.0-alpha.9`" is now "API server `5.0.0-rc.1`"
+  and "Frontend `5.0.0-rc.1`" respectively.
+* **Moved container images**. The container image names also reflect the move back into mainline:
+
+    | Before | After |
+    |:-----|:------|
+    | `docker.io/dependencytrack/hyades-apiserver` | `docker.io/dependencytrack/apiserver` |
+    | `ghcr.io/dependencytrack/hyades-apiserver` | `ghcr.io/dependencytrack/apiserver` |
+    | `docker.io/dependencytrack/hyades-frontend` | `docker.io/dependencytrack/frontend` |
+    | `ghcr.io/dependencytrack/hyades-frontend` | `ghcr.io/dependencytrack/frontend` |
+
+* **Discontinued `snapshot` container image tag**. `snapshot` tags are no longer updated to prevent
+  conflicts with version 4 of Dependency-Track, which is still receiving updates. Migrate to the
+  `5-snapshot` tag.