add json-schemas submodule

.gitmodules

+[submodule "metadata_tools/resources/json-schemas"]
+	path = metadata_tools/resources/json-schemas
+	url = git@github.com:elixir-luxembourg/json-schemas.git

README.md

 # Elixir LU metadata utilities
 
+## Clone the repository
+
+Do not forget to also **clone the submodules!**
+
+```bash
+git clone <repository-url>
+git submodule update --init
+```
+
 ## Development environment setup
 
 Create virtual environment:
 
-
 ```bash
 mkdir project_venv
 python3 -m venv project_venv
 source ./project_venv/bin/activate
 ```
 
-
 Install dependencies (single brackets are required if you are using `zsh`):
- 
+
 ```bash
 pip install -e '.[dev]'
 ```
- 
+
 ## Testing
- 
+
 Run tests with:
- 
+
 ```bash
 python setup.py test
 ```
 
-
 ## Current Version
 
 **v0.2.0-dev**
-
-
-

json-schemas @ 07c16e53

+Subproject commit 07c16e53bd41d9ba1bf969cdf091decda8b0522b