Alternative text that reflects the text in the image (#4577)

Small but important detail

docs/docs/overview/introduction.mdx

@@ -4,7 +4,7 @@ sidebar_position: 1
 
 # Introduction
 
-<img src={require('./img/feature-panel.png').default} alt="Immich" />
+<img src={require('./img/feature-panel.png').default} alt="Immich - Self-hosted photos and videos backup tool" />
 
 ## Welcome!