Docs: [DX-2939] Add new README for "x-client" package (#1923)

packages/x-client/README.md

@@ -0,0 +1,49 @@
+# X-Client
+
+### Pre-requisites
+
+Install dependencies for the workspace
+
+```bash
+yarn install
+```
+
+### Quick Start Guide
+
+All commands below need to be run in the context of the `x-client` package where this README is located. Read more about context [here](../../README.md#context).
+
+Running in `dev` mode:
+
+```bash
+yarn dev
+```
+
+Building to `dist` directory with javascript output:
+
+```bash
+yarn build
+```
+
+Running all tests:
+
+```bash
+yarn test
+```
+
+Linting:
+
+```bash
+yarn lint
+```
+
+Typechecking:
+
+```bash
+yarn typecheck
+```
+
+### About
+
+This package consists of utilities to work with the ImmutableX StarkEx-based blockchain.
+
+[Read more about the x-client package here](../../README.md#x-client)