docs: update docker usage

Co-authored-by: tangramor <[email protected]>

close slidevjs/docs#158

guide/exporting.md

@@ -131,6 +131,24 @@ This command also accept multiple entries like for the [export command](#multipl
 
 See [Static Hosting](/guide/hosting).
 
+## Exportable Docker Image
+
+To support the export feature, there is a [docker image](/guide/install#install-on-docker) (maintianed by [@tangramor](https://github.com/tangramor)) with tag **playwright**. Run following command in your work folder:
+
+```bash
+docker run --name slidev --rm -it \
+    -v ${PWD}:/slidev \
+    -p 3030:3030 \
+    -e NPM_MIRROR="https://registry.npmmirror.com" \
+    tangramor/slidev:playwright
+```
+
+Then you can use the export feature like following under your work folder:
+
+```bash
+docker exec -i slidev npx slidev export --timeout 2m --output slides.pdf
+```
+
 ## Troubleshooting
 
 ### Timeout

guide/install.md

@@ -71,9 +71,12 @@ docker run --name slidev --rm -it \
     --user node \
     -v ${PWD}:/slidev \
     -p 3030:3030 \
+    -e NPM_MIRROR="https://registry.npmmirror.com" \
     tangramor/slidev:latest
 ```
 
+**_Note_**: You can use `NPM_MIRROR` to specify a npm mirror to speed up the installation process.
+
 If your work folder is empty, it will generate a template `slides.md` and other related files under your work folder, and launch the server on port `3030`.
 
 You can access your slides from `http://localhost:3030/`
@@ -86,7 +89,6 @@ Or you can create your own slidev project to a docker image with Dockerfile:
 FROM tangramor/slidev:latest
 
 ADD . /slidev
-
 ```
 
 Create the docker image: `docker build -t myppt .`