Update docs (#27)

* Update install instructions to use go install

As per https://go.dev/doc/go-get-install-deprecation new users should use go install
instead of go get to retrieve this tool

* Include additional method for using tool with Workpaces

This should also work fine when running from a single module

README.md

@@ -10,7 +10,7 @@ While this could be considered a beginner mistake, across time, multiple package
 
 ### Get Started
 
-    $ go get github.com/jgautheron/goconst/cmd/goconst
+    $ go install github.com/jgautheron/goconst/cmd/goconst@latest
     $ goconst ./...
 
 ### Usage
@@ -40,6 +40,7 @@ Examples:
   goconst -ignore "yacc|\.pb\." $GOPATH/src/github.com/cockroachdb/cockroach/...
   goconst -min-occurrences 3 -output json $GOPATH/src/github.com/cockroachdb/cockroach
   goconst -numbers -min 60 -max 512 .
+  goconst -min-occurrences 5 $(go list -m -f '{{.Dir}}')
 ```
 
 ### Other static analysis tools

cmd/goconst/main.go

@@ -39,6 +39,7 @@ Examples:
   goconst -ignore "yacc|\.pb\." $GOPATH/src/github.com/cockroachdb/cockroach/...
   goconst -min-occurrences 3 -output json $GOPATH/src/github.com/cockroachdb/cockroach
   goconst -numbers -min 60 -max 512 .
+  goconst -min-occurrences 5 $(go list -m -f '{{.Dir}}')
 `
 
 var (