Avoid double-building, and update README.

If you moved towards using my `github-action-build` you'd use the
same script - so it would get invoked twice:

* Once by the build step
* Once by the upload step

Depreciate the build-step, but let it work for legacy for now.

README.md

@@ -1,24 +1,67 @@
 # GitHub Action for Uploading Release Artifacts
 
-This repository contains a simple GitHub Action implementation, which allows you to attach binaries to a new release.
+This repository contains a simple GitHub Action implementation, which allows you to attach binaries to a new (github) release of your repository.
 
 
 ## Enabling the action
 
 There are two steps required to use this action:
 
 * Enable the action inside your repository.
-  * This will mean creating a file `.github/workflows/release.yml` which is where the action is invoked, specifying a pattern to describe which binary-artifacts are uploaded.
-* Add your project-specific `.github/build` script.
-  * This is the script which will generate the files this action will upload.
-    * A C-project might just run `make`.
-    * A golang-based project might run `go build .` multiple times for different architectures.
+  * This will mean creating a file `.github/workflows/release.yml` which is where the action is invoked.
+  * You'll specify a pattern to describe which binary-artifacts are uploaded.
+* Ensure your binary artifacts are generated.
+  * Ideally you should do this in your workflow using another action.
+  * But if you're in a hurry you can add a project-specific `.github/build` script.
 
+## Sample Configuration: Preferred
 
-## Sample Configuration
+The following configuration file uses this action, along with another to build a project.
 
-This configuration uploads any file in your repository which matches the
-shell-pattern `puppet-summary-*`, and is defined in the file `.github/workflows/release.yml`:
+This is the preferred approach:
+
+```
+on: release
+name: Handle Release
+jobs:
+  generate:
+    name: Create release-artifacts
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout the repository
+        uses: actions/checkout@master
+      - name: Generate artifacts
+        uses: skx/github-action-build@master
+      - name: Upload artifacts
+        uses: skx/github-action-publish-binaries@master
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          args: 'example-*'
+```
+
+This is the preferred approach because it uses a pair of distinct actions,
+each having one job:
+
+* [skx/github-action-build](https://github.com/skx/github-action-build/)
+  * Generates the build artifacts.
+  * i.e. Compiles your binaries.
+* [skx/github-action-publis-binaries](https://github.com/skx/github-action-publis-binaries)
+  * Uploads the previously-generated the build artifacts.
+
+
+## Sample Configuration: Legacy
+
+In the past this action performed __both__ steps:
+
+* Generated the artifacts
+* Uploaded the artifacts
+
+That is still possible, but will be removed when actions come out of beta.
+
+For the moment you can continue to work as you did before, add the script `.github/build` to your repository, and configure this action with a pattern of files to upload.
+
+For example the following usage, defined in `.github/workflows/release.yml`, uploads files matching the pattern `puppet-summary-*`.
 
 ```
 on: release

upload-script

@@ -25,10 +25,27 @@ if [ "$IS_DRAFT" = true ]; then
   exit 0
 fi
 
-# Run the build-script
+# Is there a build-script in the repository?
 if [ -e .github/build ]; then
-    chmod 755 .github/build
-    ./.github/build
+
+    # Have we found any artifacts?
+    found=
+    for file in $*; do
+        if [ -e "$file" ]; then
+            found=1
+        fi
+    done
+
+    # OK if we have no artifacts already present, so we should
+    # invoke the build-script, which we have confirmed exists.
+    if [ -z "${found}" ]; then
+        echo "Artifacts are missing, but build-script is present."
+        echo "Building.."
+        chmod 755 .github/build
+        ./.github/build
+    else
+        echo "Artifacts are already present, so not running the build-step"
+    fi
 fi
 
 # Prepare the headers