fix readme.

Author: laixintao

README.rst

@@ -10,7 +10,9 @@ Point it at a few hosts, a whole subnet, or a host list, and get a live Textual
 
 It is built for the moment when ``ping`` is too small, dashboards are too heavy, and you just want to see what your network is doing right now.
 
-[![asciicast](https://asciinema.org/a/886189.svg)](https://asciinema.org/a/886189)
+.. image:: https://asciinema.org/a/886189.svg
+   :target: https://asciinema.org/a/886189
+   :alt: asciinema demo
 
 Why ``pingtop``
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