Add instruction on how to handle the potential linker error on Linux (#…

…47593)

Summary:
The original issue is #16683, which contains a #16683 (comment) that suggests manually un-shadowing the `ld`.

A better approach can be found at ContinuumIO/anaconda-issues#11152 (comment), which suggests that using a newer version can effectively fix this.

It took me quite some time to realize that this is in fact an issue caused by Anaconda. I think we should add it in README.

Pull Request resolved: #47593

Reviewed By: ailzhang

Differential Revision: D24866092

Pulled By: heitorschueroff

fbshipit-source-id: c1f51864d23fd6f4f63a117496d8619053e35196

README.md

@@ -149,7 +149,7 @@ They require JetPack 4.2 and above, and [@dusty-nv](https://github.com/dusty-nv)
 
 ### From Source
 
-If you are installing from source, you will need Python 3.6 or later and a C++14 compiler. Also, we highly recommend installing an [Anaconda](https://www.anaconda.com/distribution/#download-section) environment.
+If you are installing from source, you will need Python 3.6.2 or later and a C++14 compiler. Also, we highly recommend installing an [Anaconda](https://www.anaconda.com/distribution/#download-section) environment.
 You will get a high-quality BLAS library (MKL) and you get controlled dependency versions regardless of your Linux distro.
 
 Once you have [Anaconda](https://www.anaconda.com/distribution/#download-section) installed, here are the instructions.
@@ -207,6 +207,16 @@ export CMAKE_PREFIX_PATH=${CONDA_PREFIX:-"$(dirname $(which conda))/../"}
 python setup.py install
 ```
 
+Note that if you are using [Anaconda](https://www.anaconda.com/distribution/#download-section), you may experience an error caused by the linker:
+
+```plaintext
+build/temp.linux-x86_64-3.7/torch/csrc/stub.o: file not recognized: file format not recognized
+collect2: error: ld returned 1 exit status
+error: command 'g++' failed with exit status 1
+```
+
+This is caused by `ld` from Conda environment shadowing the system `ld`. You should use a newer version of Python that fixes this issue. The recommended Python version is 3.6.10+, 3.7.6+ and 3.8.1+.
+
 On macOS
 ```bash
 export CMAKE_PREFIX_PATH=${CONDA_PREFIX:-"$(dirname $(which conda))/../"}