fix: typos and changed the Sylow proof

[jfab20]

• Corrected a typo, because $G$ acts on $X$, which is a set of subsets of G, and you used the letter $X$ for an element of $X$. I changed it to $g \cdot S = \{ g s \mid s \in S \}$.
• Second of all, you don't actually need step 1 in step 2. You are just proving the statement "given some Sylow $p$-subgroup and any $p$-subgroup, this happens ...".
• The existence of $P$ is actually necessary for step $3$, because you have to take some specific $P$ and use the orbit stabilizer theorem with it, so I moved the phrase that remarks the usefulness of step 1 to step 3 and removed it from step 2.

[github-actions]

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[vEnhance]

thank you!