Update README

[koudaiii]

This pull request includes updates to the README.md file to generalize the description and usage of the Chrome extension, making it applicable to all language versions of Microsoft Learn pages rather than just the Japanese version. The most important changes include renaming the extension, updating feature descriptions, and modifying installation and usage instructions.

Updates to README.md:

• Renamed extension to "learn.microsoft.com Update Checker" and updated descriptions to reflect that it now supports all language versions. (README.md, README.mdL1-R9)
• Updated feature descriptions to highlight the comparison between the current language version and the 'en-us' version of Microsoft Learn pages. (README.md, README.mdL23-R32)
• Removed specific repository clone instructions to streamline the installation steps. (README.md, README.mdL45-L50)
• Clarified the process for loading the extension into Chrome and verifying the installation. (README.md, README.mdL61-R67)
• Updated usage instructions to reflect support for any language Microsoft Learn page. (README.md, README.mdL82-R76)

[koudaiii]

ref #21