$p\to q$ means that: $q$ will be true if $p$ is true.
Therefore $p\to q$, entails that: if $q$ is false, then $p$ cannot be true.
So if $p\to q$ then either $p$ is false or $q$ is true. $$p\to q\implies \
eg p\vee q$$
* * *
Conversely.
$\
eg p\vee q$ means that either $p$ is false or $q$ is true.
Threfore $\
eg p\vee q$ entails: if $p$ is true, then $q$ must be true.
$$\
eg p\vee q\implies p\to q$$
* * *
$$\therefore \qquad p\to q\iff \
eg p\vee q$$