Merge pull request #494 from Neverbolt/patch-1

Update plugins.md documentation for PLUGINS_DIR

Author: MWedl

docs/docs/setup/plugins.md

@@ -99,7 +99,7 @@ RUN cd /custom_plugins/myplugin1/frontend && npm install && npm run generate
 FROM syslifters/sysreptor:${SYSREPTOR_VERSION}
 # Optional: install additional dependencies
 # RUN pip install ...
-ENV PLUGIN_DIRS=${PLUGIN_DIRS}:/custom_plugins
+ENV PLUGIN_DIRS=${PLUGIN_DIRS},/custom_plugins
 COPY --from=plugin-builder /custom_plugins /custom_plugins
 ```
 
@@ -343,4 +343,4 @@ Here are some notes to get you started:
 
     [:octicons-arrow-right-24: Get help](https://github.com/Syslifters/sysreptor/discussions/categories/q-a){ target="_blank"}
 
-</div>
+</div>