IGRF model version added (#37)

* Checkout action updated

* Setup-go action updated

* More Go versions added.

* IGRF badge added.

.github/workflows/main.yml

@@ -8,12 +8,12 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go: [ '1.18', '1.19' ]
+        go: [ '1.18', '1.19', '1.20', '1.21', '1.22' ]
     name: Setup Go ${{ matrix.go }} environment
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4.1.3
       - name: Setup go
-        uses: actions/setup-go@v3
+        uses: actions/setup-go@v5
         with:
           go-version: ${{ matrix.go }}
           check-latest: true

README.md

@@ -2,6 +2,7 @@
 [![golangci-lint](https://github.com/proway2/go-igrf/actions/workflows/golangci-lint.yml/badge.svg)](https://github.com/proway2/go-igrf/actions/workflows/golangci-lint.yml)
 [![Go Reference](https://pkg.go.dev/badge/github.com/proway2/go-igrf.svg)](https://pkg.go.dev/github.com/proway2/go-igrf)
 [![Go Report Card](https://goreportcard.com/badge/github.com/proway2/go-igrf)](https://goreportcard.com/report/github.com/proway2/go-igrf)
+[![IGRF badge](https://badgen.net/static/IGRF%20model/13th/green)](https://www.ncei.noaa.gov/products/international-geomagnetic-reference-field)
 
 # go-igrf
 Pure Go IGRF (International Geomagnetic Reference Field). This is based on the existing `C` implementation. This package computes values for the geomagnetic field and secular variation for a given set of coordinates and date.