Update proxy path passthrough documentation

Includes updated create-react-app docs.

Closes #2565

src/node/proxy.ts

@@ -9,8 +9,7 @@ proxy.on("error", (error, _, res) => {
 })
 
 // Intercept the response to rewrite absolute redirects against the base path.
-// Is disabled when the request has no base path which means --proxy-path-passthrough has
-// been enabled.
+// Is disabled when the request has no base path which means /absproxy is in use.
 proxy.on("proxyRes", (res, req) => {
   if (res.headers.location && res.headers.location.startsWith("/") && (req as any).base) {
     res.headers.location = (req as any).base + res.headers.location