Fix typos and update Apple Silicon instructions in Mac install docs

[rohanmalhotracodes]

Issues addressed

Fixes #502
Fixes #503
Fixes #504
Fixes #505

Changes made

1. docs/Installing-Oppia-(Mac-OS;-Python-3).md

• “emulate” → “emulates”
• Removed outdated “Dec 2018” reference and replaced with generic timing text
• “vitual” → “virtual”
• Updated “Macs with M1 chips” wording to “Macs with Apple Silicon” (future-proofed)
• Standardized capitalization to use “Apple Silicon” consistently across the section to match Apple's official documentation.

2. docs/Installing-Oppia-(Windows;-Python-3).md

• Fixed punctuation: i.e, → i.e.,
• Corrected wording in the intro paragraph:
• “There follow…” → “The following are…”
• “one of the four” → “one of the three”
• Fixed typo: you windows system → your Windows system
• Fixed typo twice: followedby → followed by
• Capitalization fix: rdp → RDP in Step 7 heading / ToC
• Fixed capitalization: Then Open → Then open
• Fixed grammar + clarity in the wslu/PulseAudio sentence:
• added comma after “installed”
• rewrote “the starting Ubuntu app” → “the Ubuntu app on startup”
• Standardized: 64bit → 64-bit
• Removed extra word: the following the specific steps → the following specific steps
• General capitalization consistency fixes (Windows / Ubuntu / Oppia) where applicable

[rohanmalhotracodes]

@HardikGoyal2003 I have made all the required fixes. Kindly check and let me know if any other changes are required. Thanks for you time sir.

[jayam04]

LGTM!

[Meeth-webdev]

Hi @U8NWXD can you please merge this PR , Hardik told me to inform you .
Thanks !!!