Merge pull request #20 from Sensirion/add_application_notes

add application note links to readme

Author: sdmueller

.github/workflows/c.check.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: "ubuntu-22.04"
     steps:
       - uses: actions/checkout@v4
-      - uses: awalsh128/cache-apt-pkgs-action@a6c3917cc929dd0345bfb2d3feaf9101823370ad
+      - uses: awalsh128/cache-apt-pkgs-action@v1.4.3
         with:
           packages: clang-format
           version: 1.0

.github/workflows/python.build_deploy.yml

@@ -14,7 +14,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - name: Install dependencies
-        uses: awalsh128/cache-apt-pkgs-action@a6c3917cc929dd0345bfb2d3feaf9101823370ad
+        uses: awalsh128/cache-apt-pkgs-action@v1.4.3
         with: 
           packages: gcc g++ swig
           version: 1.0

README.md

@@ -20,6 +20,10 @@ corresponding `SRAW` signal as well as some additional internal states such as u
 states, the algorithm converts the raw signals in ticks into either VOC or NOx Index, respectively, and applies an adaptive
 low-pass filter.
 
+Further Information:
+- [What is Sensirion's NOx Index?](http://www.sensirion.com/resource/application_note/nox_index)
+- [What is Sensirion's VOC Index?](http://www.sensirion.com/resource/application_note/voc_index)
+
 # Quick Start
 
 Steps to calculate a VOC/NOx gas index value: