feat: Option to serve Bootstrap from the filesystem

Signed-off-by: Julien Riou <julien@riou.xyz>

src/cmd/collerd/README.md

@@ -36,6 +36,7 @@ The file format is **JSON**:
 * **enable_upload_file_button** (bool): Display the upload file button in the UI (default true)
 * **tls_cert_file** (string): Path to TLS certificate file to enable HTTPS
 * **tls_key_file** (string): Path to TLS key file to enable HTTPS
+* **bootstrap_directory** (string): Serve [Bootstrap](https://getbootstrap.com/) assets from this local directory (ex: "./node_modules/bootstrap/dist"). See **Dependencies** for details.
 
 The configuration file is not required but the service might not be exposed to the public.
 
@@ -78,4 +79,35 @@ If the note is encrypted, the encrypted value is returned (application/octet-str
 
 Errors return **500 Server Internal Error** with the **JSON** payload:
 * **message** (string): context of the error
-* **error** (string): error message
+* **error** (string): error message
+
+## Dependencies
+
+The web interface depends on:
+
+- [Bootstrap](https://getbootstrap.com/)
+- [Monaco Editor](https://github.com/microsoft/monaco-editor/)
+
+By default, those dependencies are fetched from **remote CDN** services by the client.
+
+If you would like to download them to serve them locally:
+
+```
+npm install
+```
+
+or via `make`:
+
+```
+make dependencies
+```
+
+Then configure the local directories:
+
+```json
+{
+  "bootstrap_directory": "./node_modules/bootstrap/dist"
+}
+```
+
+Downloading Monaco Editor is not supported yet.