Updated Common issues (markdown)

Common-issues.md

@@ -2,12 +2,34 @@ This page lists known solutions to common problems. If you have an solution to a
 
 ## Issues
 
+- [Error while running the add or test command](#error-when-trying-to-add-a-face-model)
 - [Camera IR emitters not turning on (or turning off very quickly)](#camera-ir-emitters-not-turning-on)
 - [Lockscreen not unlocking](#lockscreen-not-unlocking)
 - [OpenCV warning messages](#opencv-warning)
 
 ## Known solutions
 
+### Error when trying to add a face model
+
+#### Camera not configured
+
+You might get an error message like "Camera path is not configured correctly, please edit the 'device_path' config value".
+
+This probably means that you (or the installer) have not configured the camera device that Howdy should use. To fix this, open a terminal and run the following to get a list of cameras that are connected to your system:
+
+```
+find /dev/v4l/by-path/*
+```
+
+Copy one of the paths returned by the command and run `sudo howdy config` to open up the Howdy config file. Go down the file until you find a line starting `device_path`. Delete the value after the `=` and paste in the camera path you copied before. It should look like this:
+
+```
+device_path = /dev/v4l/by-path/YOUR-CAMERA-PATH-HERE
+```
+
+Multiple camera paths may show up when you run the `find` command. In that case you can repeat the step before until Howdy is using the correct IR camera.
+
+----
 ### Camera IR emitters not turning on
 
 #### Setting a specific camera resolution
@@ -45,32 +67,23 @@ no_confirmation = true
 Your lockscreen might not be running Howdy as root, which prevents Howdy from running. Setting the execution bit so every user can run Howdy might be the solution:
 
 ```
- chmod o+x /lib/security/howdy/dlib-data
+chmod o+x /lib/security/howdy/dlib-data
+```
+
+Or, alternatively:
+
+```
+sudo chmod -R 755 /lib/security/howdy/
 ```
 
 #### Howdy PAM module does not load on screensaver
 
-As reported in bug #28. In Mate/Cinnamon environments howdy may have problems running. The bug describes the way to recognize the problem (via /var/log/auth.log). If your problem is conversion, possibly the @sd65 user's solution[¹](https://github.com/Boltgolt/howdy/issues/28#issuecomment-396231042) should work:
-
-> So I have a workaround. Please note I'm using Cinnamon Screensaver (should work on Mate too).
->
-> First as you said:
->
-> `sudo chmod -R 755 /lib/security/howdy/`
->
-> Then:
->
-> `sudo howdy config`
->
-> And set `no_confirmation` to `true`.
->
-> It's crashing when sending the confirmation message, so disabling it makes the trick. :)
-
 ---
 ### Opencv Warning
-These warnings are not "serious", to disable them you need to add the lines :
+
+These warnings are not serious, to disable them add the lines to your home `.bashrc` file or equivalent:
+
 ```
 export OPENCV_LOG_LEVEL=0
 export OPENCV_VIDEOIO_PRIORITY_INTEL_MFX=0
 ``` 
-to your home `.bashrc` file (for example).