doc: add steps about signing the binary in single-executable docs

doc/api/single-executable-applications.md

@@ -33,7 +33,21 @@ tool, [postject][]:
  $ cp $(command -v node) hello
  ```
 
-3. Inject the JavaScript file into the copied binary by running `postject` with
+3. Remove the signature of the binary:
+
+ * On macOS:
+
+ ```console
+ $ codesign --remove-signature hello
+ ```
+
+ * On Windows:
+
+ ```console
+ $ signtool remove /s hello
+ ```
+
+4. Inject the JavaScript file into the copied binary by running `postject` with
  the following options:
 
  * `hello` - The name of the copy of the `node` executable created in step 2.
@@ -61,7 +75,21 @@ tool, [postject][]:
  --macho-segment-name NODE_JS
  ```
 
-4. Run the binary:
+5. Sign the binary:
+
+ * On macOS:
+
+ ```console
+ $ codesign --sign - hello
+ ```
+
+ * On Windows:
+
+ ```console
+ $ signtool sign /fd SHA256 hello
+ ```
+
+6. Run the binary:
  ```console
  $ ./hello world
  Hello, world!