Add login page initially pointing to blank page (#3592)

* Add login page initially pointing to blank page

* used the png file instead of jpg

PNG is more sharp and doesn't compress

* Update README.md

---------

Co-authored-by: Alex Demidoff <[email protected]>

Author: yashpal2104

README.md

@@ -67,7 +67,7 @@ percona/pmm-server:2
 ```
 4. Start a web browser and in the address bar enter the server name or IP address of the PMM server host.
 
-<img src="https://docs.percona.com/percona-monitoring-and-management/_images/PMM_Login.jpg" width="280">
+<img src="documentation/docs/images/PMM_Login.png" width="280" alt="PMM Login page">
 
 Enter the username and password. The defaults are username: **admin** and password: **admin**