Correct tag name & complete command suggestion (arkworks-rs#569)

* tagname should be prefixed with "v"

* suggest the full command complete with a version name

Author: mmagician

.github/release-pr-template.ejs

@@ -9,5 +9,5 @@ This is a release PR for version **<%= version.actual %>**<%
 You will still need to manually publish the cargo crate:
 
 ```
-$ make VERSION=<latest version> release
+$ make VERSION=<%= version.actual %> release
 ```

makefile

@@ -11,6 +11,6 @@ ifndef VERSION
 endif
 	git pull
 	cargo update
-	git tag $(VERSION) 
-	git push origin $(VERSION)
+	git tag v$(VERSION) 
+	git push origin v$(VERSION)
 	cargo release publish --execute --verbose