Add doc on how to compile yara

Prompted by jdnrg@

Author: jvoisin

README.md

@@ -61,8 +61,17 @@ and then passed to some dangerous function like `system`".
 ## Installation
 - [Install Yara](https://yara.readthedocs.io/en/stable/gettingstarted.html#compiling-and-installing-yara).  
 This is also possible via some Linux package managers:  
-Debian: `sudo apt-get install yara`  
-Red Hat: `yum install yara` (requires the [EPEL repository](https://fedoraproject.org/wiki/EPEL))
+  - Debian: `sudo apt-get install yara`  
+  - Red Hat: `yum install yara` (requires the [EPEL repository](https://fedoraproject.org/wiki/EPEL))
+
+You can also compile it from source:
+
+```
+git clone git@github.com:VirusTotal/yara.git
+cd yara/
+YACC=bison ./configure
+make
+```
 
 - Download php-malware-finder `git clone https://github.com/nbs-system/php-malware-finder.git`