Add language selector examples and Linguist language reference to README

[Copilot]

Users need guidance on selecting rules by language and the correct language names to use.

Changes

• Added command-line example demonstrating -s language=Go selector usage
• Added language-specific rules pattern showing how to organize and select rules for multiple languages
• Added Common Linguist Languages reference with 23 languages and correct capitalization (e.g., Go not go, TypeScript not typescript)
• Linked to GitHub Linguist canonical source for language names

Example Usage

# Select only Go-specific rules
coding-context-cli -s language=Go fix-bug

# Select Python-specific rules  
coding-context-cli -s language=Python enhance-feature

Rule files use frontmatter:

---
language: Python
---

# Python Standards
...

Original prompt

The read me should include an example of selecting rules by language. It should include a list of common Linguist languages, so that the user does not choose them incorrectly.

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