Updated plugin docs (#398)

docs/extend/plugins.md

@@ -12,13 +12,7 @@ Plugins can be added from multiple sources:
 - Custom plugins should be placed in the directory `./InvenTree/plugins`.
 - InvenTree built-in plugins are located in the directory `./InvenTree/plugin/builtin`.  
 
-Note: Plugins are discovered and loaded only when the server is started.
-
-!!! info "Enable Plugin Support"
-    To enable custom plugins, plugin support must be activated in the [server configuration](../start/config.md).
-
-!!! question "Have you tried turning it off and on again?"
-    When new plugins are installed (and activated), both the web server and background worker must be restarted.
+For further information, read more about [installing plugins](./plugins/install.md).
 
 ### Plugin Base Class
 

docs/extend/plugins/install.md

@@ -7,7 +7,42 @@ title: Installing Plugins
 
 Plugins can either be loaded from paths in the InvenTree install directory or as a plugin installed via pip. We recommend installation via pip as this enables hassle-free upgrades.
 
-### Plugin Installation File (PIP)
+### Common Issues
+
+Installing plugins can be complex! Some common issues are outlined below:
+
+#### Enable Plugin Support
+
+To enable custom plugins, plugin support must be activated in the [server configuration](../../start/config.md#plugin-options). This step must be performed by a system administrator before the InvenTree server is started.
+
+#### Restart Server
+
+Plugins are discovered and loaded only when the server is started. When new plugins are installed (and activated), both the web server and background worker must be restarted.
+
+#### Container Environments
+
+In certain container environments (such as docker), plugins are installed into an *ephemeral* virtual environment which persists only for the lifetime of the container. To allow for this, InvenTree provides a configurable setting which can automatically install plugins whenever the container is loaded.
+
+!!! tip "Check Plugins on Startup"
+    Ensure the **Check Plugins on Startup** option is enabled, when running InvenTree in a container environment!
+
+{% with id="check_plugins", url="plugin/check_on_startup.png", description="Check plugins on startup" %}
+{% include 'img.html' %}
+{% endwith %}
+
+### Installation Methods
+
+#### Builtin Plugins
+
+Builtin plugins ship in `src/InvenTree/plugin/builtin`. To achive full unit-testing for all mixins there are some sample implementations in `src/InvenTree/plugin/samples`.
+
+!!! success "Builtin Plugins"
+    Builtin plugins are always enabled, as they are required for core InvenTree functionality
+
+!!! info "Debug Only"
+    The sample plugins are not loaded in production mode.
+
+#### Plugin Installation File (PIP)
 
 Plugins installation can be simplified by providing a list of plugins in a plugin configuration file. This file (by default, *plugins.txt* in the same directory as the server configuration file) contains a list of required plugin packages.
 
@@ -23,15 +58,21 @@ Installation via PIP (using the *plugins.txt* file) provides a number of advanta
 !!! success "Auto Update"
     When the server installation is updated via the `invoke update` command, the plugins (as specified in *plugins.txt*) will also be updated automatically.
 
+!!! info "Plugin File Location"
+    The location of your plugin configuration file will depend on your [server configuration](../../start/config.md)
 
-### Builtin Plugins
+#### Web Interface
 
-Built-In plugins ship in `src/InvenTree/plugin/builtin`. To achive full unit-testing for all mixins there are some sample implementations in `src/InvenTree/plugin/samples`.
+Admin users can install plugins directly from the web interface, via the "Plugin Settings" view:
 
-!!! info "Debug Only"
-    The sample plugins are not loaded in production mode.
+{% with id="plugin_install", url="plugin/plugin_install_web.png", description="Install via web interface" %}
+{% include 'img.html' %}
+{% endwith %}
 
-### Local Directory
+!!! success "Plugin File"
+    A plugin installed via the web interface is added to the [plugins.txt](#plugin-installation-file-pip) plugin file.
+
+#### Local Directory
 
 Custom plugins can be placed in the `src/InvenTree/plugins/` directory, where they will be automatically discovered. This can be useful for developing and testing plugins, but can prove more difficult in production (e.g. when using Docker). 
 
@@ -41,7 +82,7 @@ Custom plugins can be placed in the `src/InvenTree/plugins/` directory, where th
 !!! warning "Not Recommended For Production"
     Loading plugins via the local *plugins* directory is not recommended for production. If you cannot use PIP installation (above), specify a custom plugin directory (below) or use a [VCS](https://pip.pypa.io/en/stable/topics/vcs-support/) as a plugin install source.
 
-### Custom Directory
+#### Custom Directory
 
 If you wish to install plugins from local source, rather than PIP, it is better to place your plugins in a directory outside the InvenTree source directory.