Changes to crates/core/README.md. All files

crates/core/README.md

new file mode 100644@@ -0,0 +1,15 @@+ripgrep core+------------+This is the core ripgrep crate. In particular, `main.rs` is where the `main`+function lives.++Most of ripgrep core consists of two things:++* The definition of the CLI interface, including docs for every flag.+* Glue code that brings the `grep-matcher`, `grep-regex`, `grep-searcher` and+  `grep-printer` crates together to actually execute the search.++Currently, there are no plans to make ripgrep core available as an independent+library. However, much of the heavy lifting of ripgrep is done via its+constituent crates, which can be reused independent of ripgrep. Unfortunately,+there is no guide or tutorial to teach folks how to do this yet.