Remove [--editable] in install instructions.

Use -e only in docs targeted at contributors.

If a user copy-pastes  command line with [--editable], they will hit
an error. If they don't know the --editable option, we're giving them
a choice to make before they can move forwards, but this isn't a choice
they need to make right now.

examples/README.md

@@ -10,7 +10,7 @@ Execute the following steps in a new virtual environment:
 ```bash
 git clone https://github.com/huggingface/transformers
 cd transformers
-pip install [--editable] .
+pip install .
 pip install -r ./examples/requirements.txt
 ```
 

examples/pplm/README.md

@@ -15,7 +15,7 @@ Please check out the repo under uber-research for more information: https://gith
 
 ```bash
 git clone https://github.com/huggingface/transformers && cd transformers
-pip install [--editable] .
+pip install .
 pip install nltk torchtext # additional requirements.
 cd examples/pplm
 ```

examples/summarization/README.md

@@ -10,7 +10,7 @@ The model is loaded with the pre-trained weights for the abstractive summarizati
 
 ```
 git clone https://github.com/huggingface/transformers && cd transformers
-pip install [--editable] .
+pip install .
 pip install nltk py-rouge
 cd examples/summarization
 ```