Added notes about creating parquet files and submodules in the develo…

…pment documentation (#1096)

DEVELOPMENT.md

@@ -4,6 +4,13 @@ This crate follows the standard for developing a Rust library via `cargo`.
 The CI is our "ground truth" over the state of the library. Check out the different parts of
 the CI to understand how to test the different parts of this library locally.
 
+## Git clone with submodules
+The crate comes with additional submodules to aid with testing, to ensure you have them if you plan on testing, using `--recurse-submodules` will clone the submodules alongside the repository.
+
+```bash
+git clone --recurse-submodules https://github.com/jorgecarleitao/arrow2
+```
+
 ## Testing
 
 The simplest way to test the crate is to run 
@@ -18,6 +25,41 @@ This runs the tests of the crate without features. To run all features, use
 cargo test --features full
 ```
 
+If you get warnings about parquet files not existing, you can generate the test files by using Python:
+
+```bash
+# Ubuntu: sudo apt install python3-pip python3-venv
+# Mac: brew install python3
+# Archlinux: sudo pacman -Syu python
+
+# Create a virtual environment for python, to keep dependencies contained
+python3 -m venv venv
+
+# Activate the virtual environment
+source venv/bin/activate
+
+# Make sure pip is up to date
+pip install pip --upgrade
+
+# Install pyarrow, version 6
+pip install pyarrow==6
+
+# Generate the parquet files (this might take some time, depending on your computer setup)
+python parquet_integration/write_parquet.py
+
+# Get out of venv, back to normal terminal
+deactivate
+```
+
+If you receive warnings about other files not found (IPC), ensure you have all submodules:
+```bash
+# If you didn't clone with `git clone --recurse-submodules https://github.com/jorgecarleitao/arrow2`
+git submodule update --init --recursive
+
+# Update to the latest submodules
+git submodule update --recursive --remote
+```
+
 during development of particular parts of the crate, it is usually faster
 to reduce the feature set - the tests are gated to only the relevant tests
 of that feature set. For example, if improving JSON, you can use