reduce analyzer installation time

while your solution to install all analyzer requirements looks clean and easy to understand, i've always been annoyed about how time consuming it is to watch pip & pip3 going through all requirements.txt.

I've recently tried to reduce the actual steps by deduplicating all dependencies and combining them, which speeds up the process a lot.

installation/install-guide.md

@@ -462,8 +462,10 @@ git clone https://github.com/TheHive-Project/Cortex-Analyzers
 Each analyzer comes with its own, pip compatible `requirements.txt` file. You can install all requirements with the following commands:
 
 ```
-for I in $(find Cortex-Analyzers -name 'requirements.txt'); do sudo -H pip2 install -r $I; done && \
-for I in $(find Cortex-Analyzers -name 'requirements.txt'); do sudo -H pip3 install -r $I || true; done
+for I in $(find Cortex-Analyzers -name 'requirements.txt'); do cat >> combined_requirements.txt < $I; sort -u -o combined_requirements.txt combined_requirements.txt; done
+sudo -H pip2 install -r combined_requirements.txt
+sudo -H pip3 install -r combined_requirements.txt
+rm combined_requirements.txt
 ```
 
 Next, you'll need to tell Cortex where to find the analyzers. Analyzers may be in different directories as shown in this dummy example of the Cortex configuration file (`application.conf`):