Improved grammar & punctuation in DEVELOPMENT.md (#2927)

* Improved grammar & punctuation in DEVELOPMENT.md

* Update DEVELOPMENT.md

missed a bit

* fix wording and linting

Co-authored-by: Thomas Heyenbrock <thomas.heyenbrock@gmail.com>

DEVELOPMENT.md

@@ -6,12 +6,11 @@ If you have not signed the membership agreement (it's free), you will be
 prompted by the EasyCLA bot. For more details, please see the
 [GraphQL WG repo](https://github.com/graphql/graphql-wg/tree/main/membership).
 
-1. First, you will need to have the latest git, yarn 1.16 & node 12 or greater
-   installed. OSX, Windows and Linux should all be supported as build
-   environments.
+0. First, you will need the latest `git`, `yarn` 1.16, & `node` 12 or greater.
+   macOS, Windows and Linux should all be supported as build environments.
 
-**None of these commands will work with `npm`. Please use `yarn` to develop with
-graphql**.
+**\*Note:** None of the commands below will work with `npm`. Please use `yarn`
+in this repo.\*
 
 1. Fork this repo by using the "Fork" button in the upper-right
 
@@ -30,19 +29,19 @@ graphql**.
 4. Build all interdependencies so the project you are working on can resolve
    other packages
 
-   first you'll need
+   First you'll need —
 
    ```sh
    yarn run build
    ```
 
-   you can also use
+   — or —
 
    ```sh
    yarn run build:watch
    ```
 
-   if you are focused on GraphiQL development, you can run
+   If you are focused on GraphiQL development, you can run —
 
    ```sh
    yarn run start-graphiql
@@ -60,39 +59,38 @@ graphql**.
 
 ### Fix CI issues with linting
 
-if you have prettier or eslint --fix able issues you see in CI, use yarn format:
+If you have `prettier` or `eslint --fix`-able issues you see in CI, use —
 
 `yarn format`
 
-if you see typescript build issues, do a `yarn build` locally and make sure the
-whole project references tree builds. changing interfaces can end up breaking
-their implementations.
+If you see `typescript` build issues, do a `yarn build` locally, and make sure
+the whole project references tree builds. Changing interfaces can end up
+breaking their implementations.
 
 ### Run tests for GraphiQL:
 
-- `yarn test graphiql` will run all tests for graphiql. you can also run tests
+- `yarn test graphiql` will run all tests for graphiql. You can also run tests
   from a workspace, but most tooling is at the root.
-- `yarn test --watch` will run jest with --watch
-- `yarn e2e` at the root will run the end to end suite
-- `yarn start-monaco` will launch webpack dev server for the monaco editor
-  example with GitHub API from the root. this is the fastest way to test changes
+- `yarn test --watch` will run `jest` with `--watch`
+- `yarn e2e` at the root will run the end-to-end suite
+- `yarn start-monaco` will launch `webpack` dev server for the `monaco` editor
+  example with GitHub API from the root. This is the fastest way to test changes
   to `graphql-language-service-interface`, parser, etc.
 
-if you want these commands to watch for changes to dependent packages in the
-repo, then `yarn build --watch` is what you want to run alongside either of
-these.
+If you want these commands to watch for changes to dependent packages in the
+repo, then run `yarn build --watch` alongside either of these.
 
 ### Developing for GraphiQL
 
-If you want to develop just for graphiql, you don't even need to execute
-commands from the package subdirectory at `packages/graphiql`.
+If you want to develop just for graphiql, you won't need to execute commands
+from the package subdirectory at `packages/graphiql`.
 
 First, you'll need to `yarn build` all the packages from the root.
 
 Then, you can run these commands:
 
-- `yarn start-graphiql` will launch webpack dev server for graphiql from the
-  root
+- `yarn start-graphiql` — which will launch `webpack` dev server for graphiql
+  from the root
 
 ### Developing Monaco GraphQL