Clarify install instructions to fix a pitfall (#648)

Fixes #647

README.md

@@ -76,6 +76,12 @@ See sections below for details and alternative methods.
     install_bazel_dependencies()
     ```
 
+1. Since Bazel manages a copy of the node_modules, we don't want it to discover configuration in your locally installed copy. Create a file `.bazelignore` in the root of your repo containing this line:
+
+    ```
+    node_modules
+    ```
+
 1. Create a file `BUILD.bazel` in the root of your repo, next to the `package.json` file. It can be empty for now.
 
 1. In your `package.json`, find the `"scripts"` section, or create one.

packages/typescript/docs/install.md

@@ -17,6 +17,8 @@ $ yarn add -D @bazel/typescript
 $ npm install --save-dev @bazel/typescript
 ```
 
+Watch for any peerDependency warnings - we assume you have already installed the `typescript` package from npm.
+
 Your `WORKSPACE` should declare a `yarn_install` or `npm_install` rule named `npm`.
 It should then install the rules found in the npm packages using the `install_bazel_dependencies` function.
 See https://github.com/bazelbuild/rules_nodejs/#quickstart