Update README.md

Signed-off-by: Fabiana  🧬 Campanari <113218619+FabianaCampanari@users.noreply.github.com>

Author: FabianaCampanari

README.md

@@ -89,7 +89,7 @@ The [key difference]() between sim-opt and other analytical tools is its [abilit
 
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-### An optimization problem can be represented using the `optidef` package. For example:
+### [An optimization problem]() can be represented using the `optidef` package. For example:
 
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 \begin{aligned}