Update src/02-common-principles.md

Co-authored-by: Richard Höchenberger <richard.hoechenberger@gmail.com>

src/02-common-principles.md

@@ -60,9 +60,9 @@ misunderstanding we clarify them here.
 1.  **Modality** - the category of brain data recorded by a file.
     For MRI data, different pulse sequences are considered distinct modalities,
     such as `T1w`, `bold` or `dwi`.
-    For passive recording techniques, such as EEG, MEG or iEEG,
+    For passive recording techniques, such as EEG, MEG, or iEEG,
     the technique is sufficiently uniform to define the modalities `eeg`,
-    `meg` and `ieeg`.
+    `meg`, and `ieeg`, respectively.
     When applicable, the modality is indicated in the **suffix**.
     The modality may overlap with, but should not be confused with
     the **data type**.