minor #13200 Update asset.rst (Yohann76)

This PR was submitted for the 5.0 branch but it was merged into the 3.4 branch instead (closes #13200).

Discussion
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Update asset.rst

added alt attribute

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Commits
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36a408e Update asset.rst

Author: javiereguiluz

components/asset.rst

@@ -17,7 +17,7 @@ For example:
 
     <!-- ... -->
 
-    <a href="/"><img src="/images/logo.png"></a>
+    <a href="/"><img src="/images/logo.png" alt="logo"></a>
 
 This practice is no longer recommended unless the web application is extremely
 simple. Hardcoding URLs can be a disadvantage because: