Update install.rst

Build instructions from source for debian-based distros fixed

- a git clone line was added to clarify when and where source should be
- tested on Debian GNU/Linux 11 (bullseye) / WSL2

doc/guide/install.rst

@@ -90,11 +90,12 @@ To build the app:
 
 .. code-block:: bash
 
+    git clone https://github.com/trabucayre/openFPGALoader
     mkdir build
     cd build
-    cmake ../ # add -DBUILD_STATIC=ON to build a static version
-              # add -DENABLE_UDEV=OFF to disable udev support and -d /dev/xxx
-              # add -DENABLE_CMSISDAP=OFF to disable CMSIS DAP support
+    cmake ../openFPGALoader # add -DBUILD_STATIC=ON to build a static version
+                            # add -DENABLE_UDEV=OFF to disable udev support and -d /dev/xxx
+                            # add -DENABLE_CMSISDAP=OFF to disable CMSIS DAP support
     cmake --build .
     # or
     make -j$(nproc)