[DOCS] Describe new config vars for React router (#912)

docusaurus-docs/conda-store-ui/references/config-options.md

@@ -22,11 +22,10 @@ Options:
 
 * `cookie`
 
-Lets users authenticate by logging into `conda-store`. This is the preferred method of authentication.
-
+  Lets users authenticate by logging into `conda-store`. This is the preferred method of authentication.
 * `token`
 
-Lets users utilize a token generated by `conda-store` to authenticate to the server.
+  Lets users utilize a token generated by `conda-store` to authenticate to the server.
 
 | Key                       | Value  |
 |---------------------------|--------|
@@ -54,7 +53,6 @@ Otherwise, leave blank.
 Options:
 
 * `grayscale`
-
 * `green-accent`
 
 | Key                        | Value  |
@@ -65,8 +63,47 @@ Options:
 
 * `true`
 
-Show the login icon in the top menubar.
-
+  Show the login icon in the top menubar.
 * `false`
 
-Hide the login icon in the top menubar.
+  Hide the login icon in the top menubar.
+
+| Key                   | Value  |
+|-----------------------|--------|
+|`REACT_APP_ROUTER_TYPE`| string |
+
+The type of React Router that the UI app will use.
+
+Options:
+
+* `browser`
+
+  Use the [History
+  API](https://developer.mozilla.org/en-US/docs/Web/API/History_API) to keep
+  track of app routes visited and to sync the current route with the browser URL
+  address bar. For more info, refer to
+  [createBrowserRouter](https://reactrouter.com/en/main/routers/create-browser-router)
+  in the React Router docs.
+
+* `memory`
+
+  Manage the history stack in memory instead of using the browser's history
+  ([createMemoryRouter](https://reactrouter.com/en/main/routers/create-memory-router)).
+  The [JupyterLab extension][jupyterlab-extension] configures the conda-store-ui to
+  use the memory router so that it does not conflict with JupyterLab trying to
+  manage the browser URL and history.
+
+| Key                    | Value  |
+|------------------------|--------|
+|`REACT_APP_URL_BASENAME`| string |
+
+The URL prefix for the UI app routes, if other than `/`. For example, a
+[Nebari](https://github.com/nebari-dev/nebari) deployment that serves the UI at
+`/conda-store` should set this variable to `/conda-store`. The value of this
+variable is passed directly through to React Router's
+[opts.basename](https://reactrouter.com/en/main/routers/create-browser-router#optsbasename).
+
+Only valid when React Router's "browser" router type is used, otherwise ignored.
+
+<!-- Internal links -->
+[jupyterlab-extension]: /jupyterlab-conda-store/introduction