Adding charms' libraries as Git submodules, in cases where the development is being done in a Git repository

The current documentation on how to create a Juju-based execution environment with Proxy Charms explains the directories and files that must be created for a new Juju Proxy Charm. However, the commands for adding the Charmed Operator Framework and charms.osm libraries only take into account that they will not be used in a developer's own Git repository (because the displayed commands clone the libraries repositories).

Therefore, the small modification I have done was to duplicate the set of commands related to the directories and files creation, but now with two possibilities: one for cloning the libraries' repositories, and the other to add them as Git Submodules. This way, the developer can copy and past the preferable set of commands more adapted for their needs.

03-day1.md

@@ -107,26 +107,41 @@ osm ns-create ... --config-file vars.yaml
 
 This section will focus the attention on creating a Proxy charm to configure a workload.
 
-Create a folder for the `samplecharm` in the VNFD directory, and create necessary files:
-
+Create a folder for the `samplecharm` in the VNFD directory, and create necessary files (use one of the two following ways):
+ - Given that you are developing in your local machine:
+   ```bash
+   mkdir -p charms/samplecharm/
+   cd charms/samplecharm/
+   mkdir hooks lib mod src
+   touch src/charm.py
+   touch actions.yaml metadata.yaml config.yaml
+   chmod +x src/charm.py
+   ln -s ../src/charm.py hooks/upgrade-charm
+   ln -s ../src/charm.py hooks/install
+   ln -s ../src/charm.py hooks/start
+   git clone https://github.com/canonical/operator mod/operator
+   git clone https://github.com/charmed-osm/charms.osm mod/charms.osm
+   ln -s ../mod/operator/ops lib/ops
+   ln -s ../mod/charms.osm/charms lib/charms
+   ```
+ - Given that you are developing in a Git repository:
+   ```bash
+   mkdir -p charms/samplecharm/
+   cd charms/samplecharm/
+   mkdir hooks lib mod src
+   touch src/charm.py
+   touch actions.yaml metadata.yaml config.yaml
+   chmod +x src/charm.py
+   ln -s ../src/charm.py hooks/upgrade-charm
+   ln -s ../src/charm.py hooks/install
+   ln -s ../src/charm.py hooks/start
+   git submodule add https://github.com/canonical/operator mod/operator
+   git submodule add https://github.com/charmed-osm/charms.osm mod/charms.osm
+   ln -s ../mod/operator/ops lib/ops
+   ln -s ../mod/charms.osm/charms lib/charms
+   ```
 > Go to [charms.osm](https://github.com/charmed-osm/charms.osm) if you want to learn more about how to use the charms.osm library.
 
-```bash
-mkdir -p charms/samplecharm/
-cd charms/samplecharm/
-mkdir hooks lib mod src
-touch src/charm.py
-touch actions.yaml metadata.yaml config.yaml
-chmod +x src/charm.py
-ln -s ../src/charm.py hooks/upgrade-charm
-ln -s ../src/charm.py hooks/install
-ln -s ../src/charm.py hooks/start
-git clone https://github.com/canonical/operator mod/operator
-git clone https://github.com/charmed-osm/charms.osm mod/charms.osm
-ln -s ../mod/operator/ops lib/ops
-ln -s ../mod/charms.osm/charms lib/charms
-```
-
 Include the following high level metadata in `metadata.yaml`:
 
 ```yaml