fixed:README.md

[hktalent]

$ go install github.com/zmap/zgrab2@latest
package github.com/zmap/zgrab2 is not a main package

$ go get -v -u github.com/zmap/zgrab2
....

$ cd $HOME/go/pkg/mod/github.com/zmap
 $ ls -lah
total 0
drwxr-xr-x    9 51pwn  staff   288B 10 13 10:39 .
drwxr-xr-x  162 51pwn  staff   5.1K 10 13 10:28 ..
dr-xr-xr-x    5 51pwn  staff   160B 10 13 10:25 rc2@v0.0.0-20131011165748-24b9757f5521
dr-xr-xr-x    6 51pwn  staff   192B 10 13 10:38 rc2@v0.0.0-20190804163417-abaa70531248
dr-xr-xr-x   20 51pwn  staff   640B 10 13 10:25 zcrypto@v0.0.0-20200508204656-27de22294d44
dr-xr-xr-x   23 51pwn  staff   736B 10 13 10:38 zcrypto@v0.0.0-20211005224000-2d0ffdec8a9b
dr-xr-xr-x   46 51pwn  staff   1.4K 10 13 10:25 zflags@v1.4.0-beta.1
drwxr--r--   41 51pwn  staff   1.3K 10 13 10:30 zgrab2@v0.1.7
dr-xr-xr-x   17 51pwn  staff   544B 10 13 09:35 zmap@v2.1.1+incompatible

$ cd zgrab2@v0.1.7 
$ chmod -R 744 .
$ go mod download github.com/stretchr/testify
$ make          
cd cmd/zgrab2 && go build && cd ../..
rm -f zgrab2
ln -s cmd/zgrab2/zgrab2 zgrab2

$ ls -lah zgrab2
lrwxr-xr-x  1 51pwn  staff    17B 10 13 10:30 zgrab2 -> cmd/zgrab2/zgrab2

$ ln -s `pwd`/cmd/zgrab2/zgrab2 $HOME/go/bin/zgrab2

$ zgrab2 -h
.....