docs: improve readme for docker builds

1. Add instructions to build ockam_hub image
2. Change commands to build from repository root

Author: mrinalwadhwa

tools/docker/README.md

@@ -1,18 +1,20 @@
 
+From the [root directory](../..) of the ockam codebase:
+
 ## Base
 
 ```
 docker build \
   --build-arg BASE_IMAGE=debian:10.7-slim@sha256:240f770008bdc538fecc8d3fa7a32a533eac55c14cbc56a9a8a6f7d741b47e33 \
-  --tag ockam/base:latest base
+  --tag ockam/base:latest tools/docker/base
 ```
 
 ## Builder Base
 
 ```
 docker build \
   --build-arg BASE_IMAGE=gcc:9.3.0@sha256:488373ff1b96186d48ea47f9c5eb0495b87a2ac990d15248d64d605ac7bdb539 \
-  --tag ockam/builder_base:latest base
+  --tag ockam/builder_base:latest tools/docker/base
 ```
 
 ## Builder
@@ -22,11 +24,23 @@ Build the builder:
 ```
 docker build \
   --build-arg BASE_IMAGE=ockam/builder_base:latest \
-  --tag ockam/builder:latest builder
+  --tag ockam/builder:latest tools/docker/builder
 ```
 
 Run the builder:
 
 ```
 docker run --rm -it -e LOCAL_USER_ID=$(id -u) --volume $(pwd):/work ockam/builder:latest bash
 ```
+
+## Hub
+
+```
+docker build --tag ockam/ockam_hub:latest --file tools/docker/hub/Dockerfile .
+```
+
+Run the hub:
+
+```
+docker run --rm -it ockam/ockam_hub:latest
+```