[ruby/prism] First pass at documenting information about the CRuby compiler

https://github.com/ruby/prism/commit/b575914b2f

lib/prism/prism.gemspec

@@ -24,6 +24,7 @@ Gem::Specification.new do |spec|
     "docs/build_system.md",
     "docs/building.md",
     "docs/configuration.md",
+    "docs/cruby_compilation.md",
     "docs/design.md",
     "docs/encoding.md",
     "docs/fuzzing.md",