Update README.md

[God-damnit-all]

Preview here: https://github.com/God-damnit-all/legendary/tree/patch-1

• Updated header with a centered text, "spliced" logo, and badges.
  • The legendary.svg file I added was derived from the windows icon (with many careful pixel edits), though the conversion to SVG sadly wasn't perfect.
• Adjusted all hyperlinks to point to the appropriate Heroic Games Launcher page.
• Removed nonapplicable instructions.
• Removed references of changes related to versions of Legendary from before the fork was made.
• Standardized notes & tips to use > and _ italics instead of **Note:** or **Tip:**.
  • Some notes/tips that were notes/tips previously are no longer notes/tips.
• Turned some labels into sub-headers within the Quickstart section.
• Proper capitalization for Python & Legendary except in the case of code.
• All code fences now have a lang and use three graves.
• Other minor tweaks.

[God-damnit-all]

For posterity, here's the image I did for the conversion to SVG; it only uses two colors in the palette (3A3A3A & C8C8C8):