Update go version, readme updates

.github/workflows/go.yml

@@ -19,7 +19,7 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@v4
       with:
-        go-version: '1.21.5'
+        go-version: '1.19'
 
     - name: Build
       run: go build -v ./...

README.md

@@ -1,2 +1,25 @@
 # flatsphere
-A library for converting between spherical and planar coordinates.
+
+[![GoReportCard](https://goreportcard.com/badge/owlpinetech/flatsphere)](https://goreportcard.com/report/github.com/owlpinetech/flatsphere)
+
+A [Go][] library for converting between spherical and planar coordinates.
+
+## Prerequisites
+
+- **[Go][]**: any one of the **three latest major** [releases][go-releases].
+
+## Install
+
+    go get github.com/owlpinetech/flatsphere
+
+## Usage
+
+    // converting from one projection to another
+    origProj := flatsphere.NewMercator()
+    newProj := flatsphere.NewLambert()
+    lat, lon := origProj.Inverse(origX, origY)
+    newX, newY := newProj.Project(lat, lon)
+
+## Credits
+
+Inspired by the [Map-Projections](https://github.com/jkunimune/Map-Projections) library made by [@jkunimune](https://github.com/jkunimune). Right now this library is essentially a Go-flavored port of his original Java, minus a few things to keep it focused on library use cases.

go.mod

@@ -1,3 +1,3 @@
 module github.com/owlpinetech/flatsphere
 
-go 1.21.5
+go 1.19