Updates doc for Unix build: added missing dependency byacc

Author: knst

doc/build-unix.md

@@ -13,7 +13,7 @@ Run the following commands to install required packages:
 
 ##### Debian/Ubuntu:
 ```bash
-$ sudo apt-get install curl build-essential libtool autotools-dev automake pkg-config python3 bsdmainutils
+$ sudo apt-get install curl build-essential libtool autotools-dev automake pkg-config python3 bsdmainutils byacc
 ```
 
 ##### Fedora:
@@ -158,4 +158,4 @@ If your user is in the `staff` group the limit can be raised with:
 
 The change will only affect the current shell and processes spawned by it. To
 make the change system-wide, change `datasize-cur` and `datasize-max` in
-`/etc/login.conf`, and reboot.
+`/etc/login.conf`, and reboot.