docs: update the readme

README.md

@@ -4,4 +4,61 @@
 
 Simple CLI to print diffs highlighted with test coverage status
 
+![Example Output](assets/example-output.png)
+
 </div>
+
+## Installation
+
+You can install the package with npm
+
+```bash
+npm i -g @adeattwood/diff-cov
+```
+
+You can run it directly with `npx`
+
+```bash
+npx @adeattwood/diff-cov
+```
+
+## Setup
+
+For diff-cov to get the diff to your default branch, you must set up your
+`origin/HEAD` ref. To test to see if you have this set up, run.
+
+```bash
+git rev-parse --abbrev-ref origin/HEAD
+```
+
+This should print out the origin ref to your default branch for this repo it
+will print `origin/0.x`. If you get an unknown ref error, then you will need to
+link `origin/HEAD` to your default branch with the below command.
+
+```bash
+git symbolic-ref refs/remotes/origin/HEAD refs/remotes/origin/0.x
+```
+
+> **Note**:
+> Make sure you change `0.x` for your default branch name typically `main` or
+> `development`
+
+## Usage
+
+Before you run `diff-cov` you must run your test suite with coverage and output
+a `lcov` coverage file. You must also have all your changes committed to ensure
+it's included in the output.
+
+Once you are ready to go, you can run `diff-cov` to print your diff highlighted
+with coverage status. Any line not included in the coverage report will not be
+highlighted and hit and missed lines will be colored green and red. You can use
+the `--coverageFile` flag to specify the path to your coverage report if its
+not in the default location of `./lcov.info`
+
+```bash
+diff-cov
+diff-cov --coverageFile coverage/lcov.info
+```
+
+A report is printed at the bottom and colored with a threshold of `90%`
+anything below this percentage coverage will be colored red.