Correction about anaconda in Ubuntu (#1868)

* Correction about anaconda in Ubuntu

Please correct the statement, it is just necessary to deactivate conda, rather than uninstalling it. Even compiling Caffe will cause errors because of the conda environment.

* Update 1_prerequisites.md

* Update 1_prerequisites.md

* Update 1_prerequisites.md
Co-authored-by: NGinés Hidalgo <gineshidalgo99@gmail.com>

doc/installation/1_prerequisites.md

@@ -22,7 +22,8 @@ These tips are **very important** and avoid many bugs:
 
 
 ## Ubuntu Prerequisites
-1. Ubuntu - **Anaconda should not be installed** on your system. Anaconda includes a Protobuf version that is incompatible with Caffe. Either you uninstall anaconda and install protobuf via apt-get, or you compile your own Caffe and link it to OpenPose.
+1. **Anaconda should not be installed** on your system **or should be deactivated**. Anaconda includes a Protobuf version that is incompatible with Caffe. Either you uninstall anaconda and install protobuf via apt-get, or you deactivate Conda with the command ```conda deactivate``` (twice if you are not in the base environment).
+
 2. Install **CMake GUI**:
     - Ubuntu 20: Run the command `sudo apt-get install cmake-qt-gui`.
     - Ubuntu 18: **Download and compile CMake-gui from source**. The default CMake-gui version (3.10) installed via `sudo apt-get install cmake-qt-gui` provokes some compiling errors. Required CMake version >= 3.12.