Build documentation update, moved to gitlab

doc/GET_SOURCES.md

+# The OpenAirInterface repository
+
+The OpenAirInterface software can be obtained from our gitLab
+server. You will need a git client to get the sources. The repository
+is currently used for main developments.
+
+## Prerequisite
+
+You need to install the subversion/git using the following commands:
+
+```shell
+sudo apt-get update
+sudo apt-get install subversion git
+```
+
+## Using EURECOM Gitlab
+
+The [openairinterface5g repository](https://gitlab.eurecom.fr/oai/openairinterface5g.git)
+holds the source code for (eNB RAN + UE RAN).
+
+For legal issues (licenses), the core network (EPC) source code is now moved away from
+the above openairinterface5g git repository. This EPC code is now splitted into two git
+projects ([openair-cn](https://gitlab.eurecom.fr/oai/openair-cn.git) with apache license
+and [xtables-addons-oai](https://gitlab.eurecom.fr/oai/xtables-addons-oai.git) with GPL license).
+
+Configure git with your name/email address (only important if you are developer and want to checkin code to Git):
+
+```shell
+git config --global user.name "Your Name"
+git config --global user.email "Your email address"
+```
+
+- Add a certificate from gitlab.eurecom.fr to your Ubuntu 14.04 installation:
+
+```shell
+echo -n | openssl s_client -showcerts -connect gitlab.eurecom.fr:443 2>/dev/null | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' | sudo tee -a /etc/ssl/certs/ca-certificates.crt
+```
+
+- Disable certificate check completely if you do not have root access to /etc/ssl directory
+
+```shell
+git config --global http.sslverify false
+```
+
+### In order to checkout the Git repository (for OAI Users without login to gitlab server)
+
+Checkout RAN repository (eNB RAN + UE RAN):
+
+```shell
+git clone https://gitlab.eurecom.fr/oai/openairinterface5g.git
+```
+
+Checkout EPC (Core Network) repository:
+
+```shell
+git clone https://gitlab.eurecom.fr/oai/openair-cn.git
+```
+
+Optionally (openair-cn build script can install it for you):
+
+```shell
+git clone https://gitlab.eurecom.fr/oai/xtables-addons-oai.git
+```
+
+### In order to checkout the Git repository (for OAI Developers/admins with login to gitlab server)
+
+Please send email to {openair_tech (AT) eurecom (DOT) fr} to be added to the repository
+as a developer (only important for users who want to commit code to the repository). If
+you do not have account on gitlab.eurecom.fr, please register yourself to gitlab.eurecom.fr.
+
+* Checkout with using ssh keys:
+   * You will need to put your ssh keys in https://gitlab.eurecom.fr/profile/keys
+     to access to the git repo. Once that is done, checkout the git repository using:
+   * `git clone git@gitlab.eurecom.fr:oai/openairinterface5g.git`
+* Checkout with user name/password prompt:
+   * `git clone https://YOUR_USERNAME@gitlab.eurecom.fr/oai/openairinterface5g.git`
+   * `git clone https://YOUR_USERNAME@gitlab.eurecom.fr/oai/openair-cn.git`
+   * `git clone https://YOUR_USERNAME@gitlab.eurecom.fr/oai/xtables-addons-oai.git` (optional, openair-cn build script can do it for you)
+
+## Which branch to checkout?
+
+On the RAN side:
+
+* **master**: This branch is targeted for the user community. Since January 2019, it is also subject to a Continuous Integration process. The update frequency is about once every 2-3 months. We are also performing bug fixes on this branch.
+* **develop**: This branch contains recent commits that are tested on our CI test bench. The update frequency is about once a week.
+
+Please see the work flow and policies page :
+
+https://gitlab.eurecom.fr/oai/openairinterface5g/wikis/oai-policies-home
+
+you can find the latest stable tag release here :
+
+https://gitlab.eurecom.fr/oai/openairinterface5g/tags
+
+The tag naming conventions are :
+
+- On `master` branch: **v1.`x`.`y`** where
+  * `x` is the minor release number, incremented every 2-3 months when we are merging `develop` into `master` branch.
+  * `y` is the maintenance number, starting at 0 when we do a minor release and being incremented when a bug fix is incorporated into `master` branch.
+- On `develop` branch **`yyyy`.w`xx`**
+  * `yyyy` is the calendar year
+  * `xx` the week number within the year
+

doc/RUNMODEM.md

+# Running OAI softmodem
+
+After you have [built the softmodem executables](BUILD.md) you can go to the build directory `cmake_targets/lte_build_oai/build/` and start testing some use cases. 
+
+## rf simulator
+
+​    This is the easiest use-case to setup and test,  you need two x86 PCs, 4 cores and 3GHz CPU should be enough
+
+## Monolithic eNodeB with USRP radio head
+
+1. ##  
+