docs: Add brief docs for developing scip-ruby.

Author: varungandhi-src

README.md

@@ -4,6 +4,12 @@
 
 # Sorbet
 
+NOTE: This code is in Sourcegraph's fork of Sorbet, modified to add support
+for emitting SCIP indexes. See scip-ruby.md for details on running tests etc.
+The original README follows below.
+
+---
+
 This repository contains Sorbet, a fast, powerful type checker designed for Ruby.
 It aims to be easy to add to existing codebases with gradual types, and fast to
 respond with errors and suggestions.

scip-ruby.md

@@ -0,0 +1,34 @@
+# scip-ruby
+
+## Building
+
+```
+./bazel build //main:scip-ruby --config=dbg
+```
+
+For more information about configurations, see the main [README](./README.md).
+
+## IDE Integration
+
+Generate `compile_commands.json` as per the main [README](./README.md),
+and point your editor to it.
+
+## Generating a SCIP index
+
+NOTE: The binary will be somewhere under `bazel-out` depending on the exact config.
+
+```
+scip-ruby myfile.rb --index-file index.scip
+```
+
+## Running SCIP tests
+
+```
+./bazel test //test/scip --config=dbg
+```
+
+Updating snapshots
+
+```
+./bazel test //test/scip:update --config=dbg
+```