[WIP] Add guideline on branches to CONTRIBUTING.md

Proposal per discussion in codemeta#347 (not finalize yet). In general:

- `develop` for vocabulary changes
- `master` for non-vocabulary changes

This will resolve codemeta#347

CONTRIBUTING.md

@@ -1,15 +1,21 @@
 # Contribution Guide
 
-This guide is intended for people who want to contribute to content of the Git repository.
+This guide is intended for people who want to contribute to content of CodeMeta Git repository.
 
 ## Layout
 
 The repository is laid out as such:
 
-* `scripts/`: Python scripts to manipulate the crosswalk table
-* `properties_description.csv`: A CSV files with human-readable information about each CodeMeta property.
-* `crosswalks/*.csv`: Two-column CSV files, that map between CodeMeta's properties and platform-specific terms.
-* `crosswalk.csv`: An aggregated table of all CSV files mentionned above; intended to be the main resource for readers.
+- `scripts/`: Python scripts to manipulate the crosswalk table.
+- `properties_description.csv`: A CSV files with human-readable information about each CodeMeta property.
+- `crosswalks/*.csv`: Two-column CSV files, that map between CodeMeta's properties and platform-specific terms.
+- `crosswalk.csv`: An aggregated table of all CSV files mentionned above; intended to be the main resource for readers. Meant to be generated by a script and not be manually edited.
+
+The repository has two major branches:
+
+- `develop`: Any contribution that will change CodeMeta vocabulary should target this branch. Adding a new property, amending or removing an existing property will change the vocabulary.
+- `master`: All other non-vocabulary changes, including mapping and crosswalk updates, should target this branch.
+  - A minor amendment to a property *decription* (not property *name* or *type*) can target this branch as well, as long as it does not change the semantic of the property.
 
 ## About pull requests
 
@@ -20,7 +26,7 @@ Do not commit changes to `crosswalk.csv`, as these will very likely create confl
 ## Editing an existing mapping
 
 Open the CSV file in `crosswalks/` that contains your mapping.
-You may change the second column (ie. what comes after the comma on each line) to match the terms of the platform your new mapping covers.
+You may change the second column (i.e. what comes after the comma on each line) to match the terms of the platform your new mapping covers.
 
 Then, run `scripts/aggregate.py`. This will build the new `crosswalk.csv` using the updated version of your mapping; and raise an error if you made a mistake (such as editing the first column).
 
@@ -30,14 +36,18 @@ You can now commit your changes and send a pull request. Don't forget to **exclu
 
 To add a new platform mapping to CodeMeta, you have to add a new CSV file to `crosswalks/`. The filename is free-form, but please to avoid non-ASCII characters. The name is not used to build the aggregated table.
 
-You may copy any other CSV file from `crosswalks/` to write yours; the refer to the "Editing an existing mapping" section.
+You may copy any other CSV file from `crosswalks/` to write yours; then refer to the "Editing an existing mapping" section.
 
 ## Adding a new CodeMeta property
 
+1) **Adding the new property:**
 To do so, you should first edit `properties_description.csv` and add a line with the appropriate cells there; and edit `codemeta.jsonld` as well.
 
-Then, add that line to each `crosswalks/*.csv` file, in the same position as in `properties_description.csv`.
+2) **Update all existing mappings with the new property name:**
+Add the new property name to each `crosswalks/*.csv` file, in the same position as in `properties_description.csv`.
 
-Then, run `scripts/aggregate.py`. This will build the new `crosswalk.csv` with the new property; and raise an error if you made a mistake (such as editing the first column).
+3) **Test:**
+Run `scripts/aggregate.py`. This will build the new `crosswalk.csv` with the new property; and raise an error if you made a mistake (such as editing the first column).
 
+4) **Commit changes:**
 You may then create a commit and send a pull request. Don't forget to **exclude** `crosswalk.csv` from the commit.