Add an upper bound to the ffmpeg version installed in documentation (#861)

Author: traversaro

CONTRIBUTING.md

@@ -30,7 +30,7 @@ Start by installing the **nightly** build of PyTorch following the
 Then, the easiest way to install the rest of the dependencies is to run:
 
 ```bash
-conda install cmake pkg-config pybind11 ffmpeg -c conda-forge
+conda install cmake pkg-config pybind11 "ffmpeg<8" -c conda-forge
 ```
 
 ### Clone and build

README.md

@@ -114,9 +114,9 @@ ffmpeg -f lavfi -i \
    easy way to install it is to use `conda`:
 
    ```bash
-   conda install ffmpeg
+   conda install "ffmpeg<8"
    # or
-   conda install ffmpeg -c conda-forge
+   conda install "ffmpeg<8" -c conda-forge
    ```
 
 3. Install TorchCodec:
@@ -157,9 +157,9 @@ format you want. Refer to Nvidia's GPU support matrix for more details
    easy way to install it is to use `conda`:
 
    ```bash
-   conda install ffmpeg
+   conda install "ffmpeg<8"
    # or
-   conda install ffmpeg -c conda-forge
+   conda install "ffmpeg<8" -c conda-forge
    ```
 
    If you are building FFmpeg from source you can follow Nvidia's guide to