Update documentation about how to install YARA.
Update documentation about how to install YARA.

* Add pkg-config to the list of packages that must be installed
* Move instructions for using vcpkg to its own section

wxsBSD/yara,VirusTotal/yara,hillu/yara,hillu/yara,plusvic/yara,pombredanne/yara,plusvic/yara,cblichmann/yara,pombredanne/yara,cblichmann/yara,VirusTotal/yara,wxsBSD/yara,pombredanne/yara,pombredanne/yara,VirusTotal/yara,plusvic/yara,VirusTotal/yara,hillu/yara,hillu/yara,hillu/yara,cblichmann/yara,plusvic/yara,pombredanne/yara,wxsBSD/yara,wxsBSD/yara,cblichmann/yara,VirusTotal/yara,wxsBSD/yara,cblichmann/yara,plusvic/yara