Merge pull request #367 from Paraphraser/20210614-gettingStarted-master

Changes to "getting started" documentation - master branch

Author: Slyke

docs/Getting-Started.md

@@ -113,7 +113,9 @@ If you are still running on gcgarner/IOTstack and need to migrate to SensorsIot/
 
 * [Migrating IOTstack from gcgarner to SensorsIot](./gcgarner-migration.md).
 
-## <a name="recommendedPatches"> recommended system patch </a>
+## <a name="recommendedPatches"> recommended system patches </a>
+
+### <a name="patch1DHCP"> patch 1 – restrict DHCP </a>
 
 Run the following commands:
 
@@ -124,6 +126,17 @@ $ sudo reboot
 
 See [Issue 219](https://github.com/SensorsIot/IOTstack/issues/219) and [Issue 253](https://github.com/SensorsIot/IOTstack/issues/253) for more information.
 
+### <a name="patch2DHCP"> patch 2 – update libseccomp2</a>
+
+If you don't have this patch in place, Docker images that are based on Alpine will fail if an image's maintainer updates to [Alpine 3.13](https://wiki.alpinelinux.org/wiki/Release_Notes_for_Alpine_3.13.0#time64_requirement).
+
+```
+$ sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 04EE7237B7D453EC 648ACFD622F3D138
+$ echo "deb http://httpredir.debian.org/debian buster-backports main contrib non-free" | sudo tee -a "/etc/apt/sources.list.d/debian-backports.list"
+$ sudo apt update
+$ sudo apt install libseccomp2 -t buster-backports
+```
+
 ## <a name="aboutSudo"> a word about the `sudo` command </a>
 
 Many first-time users of IOTstack get into difficulty by misusing the `sudo` command. The problem is best understood by example. In the following, you would expect `~` (tilde) to expand to `/home/pi`. It does:
@@ -237,6 +250,38 @@ The old and new menus differ in the options they offer. You should come back and
 
 ## <a name="switchingMenus"> switching menus </a>
 
+At the time of writing, IOTstack supports three menus:
+
+* "Old Menu" on the `old-menu` branch. This was inherited from [gcgarner/IOTstack](https://github.com/gcgarner/IOTstack).
+* "New Menu" on the `master` branch. This is the current menu.
+* "New New Menu" on the `experimental` branch. This is under development.
+
+With a few precautions, you can switch between git branches as much as you like without breaking anything. The basic check you should perform is:
+
+```
+$ cd ~/IOTstack
+$ git status
+```
+
+Check the results to see if any files are marked as "modified". For example:
+
+```
+modified:   .templates/mosquitto/Dockerfile
+```
+
+Key point:
+
+* Files marked "untracked" do not matter. You only need to check for "modified" files because those have the potential to stop you from switching branches cleanly.
+
+The way to avoid potential problems is to move any modified files to one side and restore the unmodified original. For example:
+
+```
+$ mv .templates/mosquitto/Dockerfile .templates/mosquitto/Dockerfile.save
+$ git checkout -- .templates/mosquitto/Dockerfile
+```
+
+When `git status` reports no more "modified" files, it is safe to switch your branch.
+
 ### <a name="menuMasterBranch"> current menu (master branch) </a>
 
 ```