Fixes and minor additions

Author: astrojuanlu

sessions/02_layout-unit-tests.ipynb

@@ -45,12 +45,13 @@
     "To put yourself in a clean state again, you have to:\n",
     "\n",
     "1. Click \"remove branch\" in the pull request (don't click \"remove fork\"!)\n",
-    "2. `git checkout master` to go back to `master`\n",
+    "2. `git checkout master` (go back to `master`)\n",
     "3. `git fetch origin` (**never, ever use `git pull` unless you know exactly what you're doing**)\n",
-    "4. `git merge --ff-only origin master` (this will update your local `master` with `origin/master`, and fail if you accidentally made any commit in `master`)\n",
-    "5. `git fetch -p <username>` :star2: this will acknowledge the removal of the branch :star2:\n",
-    "6. `git push <username> master` (this will update your fork with respect to `origin`)\n",
-    "7. `git checkout -b new-branch` to start working in the new feature!\n",
+    "4. `git merge --ff-only origin master` (update your local `master` with `origin/master`, and fail if you accidentally made any commit in `master`)\n",
+    "5. `git fetch -p <username>` (✨ acknowledge the removal of the remote branch ✨)\n",
+    "6. `git branch -d old-branch` (remove the old branch)\n",
+    "7. `git push <username> master` (update your fork with respect to `origin`)\n",
+    "8. `git checkout -b new-branch` (start working in the new feature!)\n",
     "\n",
     "This process **has to be repeated after every pull request**.\n",
     "\n",
@@ -114,7 +115,7 @@
     "```\n",
     "[metadata]\n",
     "name = my_package\n",
-    "version = 0.1.0\n",
+    "version = 0.1.dev0\n",
     "\n",
     "# Magic! Don't touch below this line\n",
     "[options]\n",
@@ -140,6 +141,22 @@
     "This is an alternative to modifying the `PYTHONPATH` environment variable (see first session)."
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "### Version numbers\n",
+    "\n",
+    "* Version numbers for Python packages are explained in [PEP 440](https://www.python.org/dev/peps/pep-0440/)\n",
+    "* For libraries, the most widely used convention is [semantic versioning](https://semver.org/): `X.Y.Z`\n",
+    "  - `Z` **must** be incremented if only backwards compatible bug fixes are introduced (a bug fix is defined as an internal change that fixes incorrect behavior)\n",
+    "  - `Y` **must** be incremented every time there is new, backwards-compatible functionality\n",
+    "  - `X` **must** be incremented every time there are backwards-incompatible changes\n",
+    "* Between releases, the version should have the `.dev0` suffix\n",
+    "* Recommendation: start with `0.1.dev0` (development version), then make a `0.1.0` release, then progress to `0.1.1` for quick fixes and `0.2.0` for new functionality, and when you want to make a promise of *relative* stability jump to `1.0.0`\n",
+    "* For applications, other conventions are more appropriate, like [calendar versioning](http://calver.org/): `[YY]YY.MM.??"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},