re-introduce install instructions with to releases

Installation instructions were included with releases until 0.16.0, but lost after that, perhaps with release automation moving to GitHub. These instructions are still referenced in the README.md as being available in Releases, so this PR reintroduces them.

Fixes #1648


Signed-off-by: Anthony Goddard <[email protected]>

.goreleaser.yml

@@ -58,11 +58,73 @@ release:
 
     New v{{ .Version }} release!
   footer: |
-    ## Release Notes
+    ## Installation Instructions
+
+    ### Cluster-side
+
+    Install the SealedSecret CRD and server-side controller into the `kube-system` namespace:
+
+    ```sh
+    kubectl apply -f https://github.com/bitnami-labs/sealed-secrets/releases/download/v{{ .Version }}/controller.yaml
+    ```
+
+    ### Client-side
+
+    Install the client-side tool into `/usr/local/bin/`:
+
+    **Linux x86_64:**
+    ```sh
+    curl -OL "https://github.com/bitnami-labs/sealed-secrets/releases/download/v{{ .Version }}/kubeseal-{{ .Version }}-linux-amd64.tar.gz"
+    tar -xvzf kubeseal-{{ .Version }}-linux-amd64.tar.gz kubeseal
+    sudo install -m 755 kubeseal /usr/local/bin/kubeseal
+    ```
+
+    **macOS:**
+    The `kubeseal` client is available on [homebrew](https://formulae.brew.sh/formula/kubeseal):
+
+    ```sh
+    brew install kubeseal
+    ```
+
+    **MacPorts:**
+
+    The `kubeseal` client is available on [MacPorts](https://ports.macports.org/port/kubeseal/summary):
+
+    ```sh
+    port install kubeseal
+    ```
 
-    Please read the [RELEASE_NOTES](https://github.com/bitnami-labs/sealed-secrets/blob/main/RELEASE-NOTES.md) which contain among other things important information for who is upgrading from previous releases.
+    #### Nixpkgs
 
+    The `kubeseal` client is available on [Nixpkgs](https://search.nixos.org/packages?channel=unstable&show=kubeseal&from=0&size=50&sort=relevance&type=packages&query=kubeseal): (**DISCLAIMER**: Not maintained by bitnami-labs)
+
+    ```sh
+    nix-env -iA nixpkgs.kubeseal
+    ```
+
+    **Other OS/Arch:**
+    Binaries for other OS/arch combinations are attached to this release below.
+
+    If you just want the latest client tool, it can be installed into
+    `$GOPATH/bin` with:
+
+    ```sh
+    go install github.com/bitnami-labs/sealed-secrets/cmd/kubeseal@main
+    ```
+
+    You can specify a release tag or a commit SHA instead of `main`.
+
+    The `go install` command will place the `kubeseal` binary at `$GOPATH/bin`:
+
+    ```sh
+    $(go env GOPATH)/bin/kubeseal
+    ```
+
+    ## Release Notes
+
+    Please read the [RELEASE_NOTES](https://github.com/bitnami-labs/sealed-secrets/blob/main/RELEASE-NOTES.md) which contain among other things important information for those upgrading from previous releases.
     ## Thanks!
+
   extra_files:
     - glob: ./controller.yaml
     - glob: ./controller-norbac.yaml