change: default target make just does go build, add make snapshot

- this way the default target does not need `goreleaser`

Author: agilgur5

Makefile

@@ -8,7 +8,7 @@ GOVERSION := $$(go version)
 # keep docopts: as first target for development
 
 docopts: docopts.go Makefile
-	GOVERSION=$(GOVERSION) goreleaser build --rm-dist --snapshot --single-target -o $@
+	go build -o $@
 
 install_builddep:
 	go mod tidy
@@ -35,5 +35,8 @@ README.md: examples/legacy_bash/rock_hello_world.sh examples/legacy_bash/rock_he
 clean:
 	rm -f docopts-* docopts README.tmp dist/*
 
-release: clean all test
+snapshot: install_builddep
+	GOVERSION=$(GOVERSION) goreleaser build --rm-dist --snapshot --single-target -o $@
+
+release: clean all test snapshot
 	GOVERSION=$(GOVERSION) goreleaser release

README.md

@@ -374,6 +374,7 @@ you have Go installed. Or find a local golang developer that you
 trust and ask her, in exchange for a beer or two, if she could build it for you. ;)
 
 local build:
+(also done with our Makefile default target: `make`)
 
 ```
 go build docopts.go
@@ -385,7 +386,7 @@ cross compile for 32 bit:
 env GOOS=linux GOARCH=386 go build docopts.go
 ```
 
-or via Makefile (note that this installs extra, development only dependencies):
+or via Makefile:
 
 ```
 make all