updated README from warrior branch

README.md

-Note for developers: **To have SSH access to all Elphel's repositories clone this project using SSH**
-
-Note for users: **Some already built firmware images are available [here](http://community.elphel.com/files/393/). Also check [User Manual](https://wiki.elphel.com/wiki/Tmp_manual).**
-
 # elphel393
-The project contains scripts for fetching and setting up build environment that will generate firmware images for Elphel393 camera systems.
 
-It clones and configures several individual repositories, such as
-* https://git.elphel.com/Elphel/linux-elphel
-* https://git.elphel.com/Elphel/x393
-* http://git.yoctoproject.org
-* http://git.openembedded.org
-* https://github.com/Xilinx/meta-xilinx
-* https://git.elphel.com/Elphel/meta-elphel393
+Scripts for setting up development environment to build firmware for Elphel393 camera systems.
+
+Prebuilt firmware: [community.elphel.com/files/393/](http://community.elphel.com/files/393/).
 
-The same script (*setup.py*) pulls updates from these repositories
+## Requirements
 
-### Get environment
-#### Dependencies
+### for Kubuntu 20.04 
 * poky might require installing some packages, please check with the [Yocto Poky Manual](http://www.yoctoproject.org/docs/2.0/mega-manual/mega-manual.html)
-* extra requirement
+* extra packages:
 
 ```sh
-$ sudo apt install python-numpy
+# in Kubuntu 20.04 this will install python2 which is used by poky[warrior]
+$ sudo apt install python python-numpy python3-numpy
+# below fixes missing error when compiling the kernel: missing "openssl/bio.h":
+$ sudo apt install libssl-dev
 ```
 
-#### Get sources
+### for Kubuntu 16.04/18.04
+* same as for Kubuntu 20.04
+* run setup.py then roll back [meta-elphel393](https://git.elphel.com/Elphel/meta-elphel393) to [6e0687d745e8962ec979e59ed600203c97d92cff](https://git.elphel.com/Elphel/meta-elphel393/commit/6e0687d745e8962ec979e59ed600203c97d92cff)
+
+### Setup
 ```sh
 $ ./setup.py
 ```
 
-### Build targets
+### Build
 ```sh
 $ cd poky
 $ . ./oe-init-build-env
 $ bitbake u-boot device-tree linux-xlnx core-image-elphel393
 ```
 
-* the results are in *poky/build/tmp/deploy/images/elphel393/*
+* the results are in *bootable-images/*
 * for more details, read [**this guide**][1] at [https://wiki.elphel.com][1]
 
 [1]: http://wiki.elphel.com/index.php?title=Poky_2.0_manual
@@ -60,16 +57,3 @@ $ (if changes in the rootfs and the kernel) bitbake core-image-elphel393
 ### Support
 
 support-list@support.elphel.com
-
-### Note 1: Switching between GIT protocols (SSH or HTTPS)
-
-To have access to related Elphel's projects over **SSH** clone this project using **SSH**.
-
-For **HTTPS** clone with **HTTPS**.
-
-To change git protocol for all Elphel's projects - change the *remote* of this project accordingly, then run *setup.py*:
-```sh
-$ git remote -v
-$ git remote set-url ...
-$ ./setup.py
-```
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