update README.md

Author: stang

README.md

@@ -1,3 +1,45 @@
 # git-remote-https+iap
 
 An open source [`git-remote-helper`](https://git-scm.com/docs/git-remote-helpers) that handles authentication for [GCP Identity Aware Proxy](https://cloud.google.com/iap).
+
+## Getting Started
+
+### Installing
+
+- Download pre-compiled binaries from [`our release page`](https://github.com/stang/ci-sandbox/releases/).
+- Install `git-remote-https+iap` binary onto the system `$PATH`
+- Run `GIT_IAP_VERBOSE=1 git-remote-https+iap install`
+
+### Configuring
+
+- [Generate OAuth credentials FOR THE HELPER](https://cloud.google.com/iap/docs/authentication-howto#authenticating_from_a_desktop_app)[1]
+- Configure the IAP protected repositories:
+
+```
+git-remote-https+iap configure \
+  --repoURL=https://git.domain.acme/demo/hello-world.git \
+  --helperID=xxx \
+  --helperSecret=yyy \
+  --clientID=zzz
+```
+
+**Notes**:
+* In the example above, `xxx` and `yyy` are the OAuth credentials FOR THE HELPER, that needs to be created as instructed [here](https://cloud.google.com/iap/docs/authentication-howto#authenticating_from_a_desktop_app). `zzz` is the OAuth client ID that has been created when your Identity Aware Proxy instance has been created.
+* All repositories served on the same domain (`git.domain.acme`) would share the same configuration
+
+
+[1]: This needs to be done only once per _organisation_. While [these credentials are not treated as secret](https://developers.google.com/identity/protocols/oauth2#installed) and can be shared within your organisation, [it seem forbidden to publish them in any open source project](https://stackoverflow.com/questions/27585412/can-i-really-not-ship-open-source-with-client-id).
+
+### Usage
+
+Once your domain has been configured, you should be able to use `git` as you would normally do, without thinking about the IAP layer.
+
+```
+$ git clone https://git.domain.acme/demo/hello-world.git
+```
+
+> If you are using [`git-lfs`](https://git-lfs.github.com/), the minimal version requirement is [`>= v2.9.0`](https://github.com/git-lfs/git-lfs/releases/), which introduced support of HTTP cookies.
+
+### Troubleshoot
+
+If needed, you can set the `GIT_IAP_VERBOSE=1` environment variable in order to increase the verbosity of the logs.