README: add localhost guide

README.md

@@ -57,6 +57,26 @@
 - **nightly**:
     - Instance: https://idhub-nightly.demo.pangea.org
     - Motivation: regenerated on each day at 4:00 AM
+- **localhost-pair**:
+    - Instances:
+        - http://localhost
+        - http://idhub2
+    - Motivation: test locally an OIDC scenario
+- **localhost-trio**:
+    - Instances:
+        - http://localhost
+        - http://idhub2
+        - http://idhub3
+    - Motivation: test locally a more complex OIDC scenario (similar to pilot no9b)
+
+### Details on localhost config
+
+You can test all the features in localhost. It was tested on Debian GNU/Linux 12 (bookworm)
+
+- on host machine install nginx and docker
+- nginx acts as a reverse proxy is used to get into docker containers (same approach applies to deployed pilots and instances)
+    - see [nginx-localhost.site]() for the nginx site config
+- add at the end of `/etc/hosts` a line with: `127.0.0.1       idhub2 idhub3` so you make work the DNS resolution locally
 
 ## Installation