Add python2 dependency

`repo` still requires python2
diff --git a/blissroms/build-guide.md b/blissroms/build-guide.md
index c2e6a9a..7e2e7c2 100644
--- a/blissroms/build-guide.md
+++ b/blissroms/build-guide.md
@@ -39,7 +39,7 @@
 
 For Ubuntu 18.x (or newer):
 
-    sudo apt install bison build-essential curl flex git gnupg gperf liblz4-tool libncurses5-dev libsdl1.2-dev libwxgtk3.0-dev libxml2 libxml2-utils lzop maven pngcrush schedtool squashfs-tools xsltproc zip zlib1g-dev g++-multilib gcc-multilib lib32ncurses5-dev lib32readline-dev lib32z1-dev libc6-dev-i386 x11proto-core-dev libx11-dev ccache libgl1-mesa-dev unzip
+    sudo apt install bison build-essential curl flex git gnupg gperf liblz4-tool libncurses5-dev libsdl1.2-dev libwxgtk3.0-dev libxml2 libxml2-utils lzop maven pngcrush schedtool squashfs-tools xsltproc zip zlib1g-dev g++-multilib gcc-multilib lib32ncurses5-dev lib32readline-dev lib32z1-dev libc6-dev-i386 x11proto-core-dev libx11-dev ccache libgl1-mesa-dev unzip python
 
 ### Install source code tools