Document how to install cellxgene prepare

after pr #887 merged

docs/data.md

@@ -14,6 +14,14 @@ description: Data
 
 `cellxgene prepare` is not meant as a way to formally process or analyze your data. It's simply a utility for quickly wrangling your data into cellxgene-compatible format and computing a "vanilla" embedding so you can try out `cellxgene` and get a general sense of a dataset.
 
+#### How do I install `cellxgene prepare`?
+
+The `cellxgene prepare` command is an optional install that you can install alongside `cellxgene launch` by running
+
+```
+pip install cellxgene[prepare]
+```
+
 #### What input formats does it accept?
 
 Currently, we accept `h5ad` and `loom` files, as well as `10x` directories, and are hoping to accept more formats in the future.
@@ -52,9 +60,9 @@ Let's look at what `prepare` is doing to our data, and how each step relates to
 
 # Example datasets to use with cellxgene
 
-
-**To download and use these datasets, run:**  
-`curl -O [URL]`  
+
+**To download and use these datasets, run:**  
+`curl -O [URL]`  
 `unzip [filename.zip]`  
 `cellxgene launch [filename.h5ad] --open`
 

docs/faq.md

@@ -12,6 +12,8 @@ Currently, you can go straight into `cellxgene launch` with your own analyzed da
 
 If your data is in a different format, and/or you still need to perform dimensionality reduction and clustering, `cellxgene` can do that for you with the `prepare` command. `cellxgene prepare` runs `scanpy` under the hood and can read in any format that is currently supported by `scanpy` (including mtx, loom, and more listed [here](https://scanpy.readthedocs.io/en/latest/api/index.html#reading)).
 
+To add `cellxgene prepare` to your cellxgene installation run `pip install cellxgene[prepare]`. 
+
 The output of `cellxgene prepare` is a h5ad file with your computed clusters and tsne/umap projections that can be used in `cellxgene launch`.
 
 #### I have a directory of 10X-Genomics data with _mtx_ files and I've never used _scanpy_, can I use _cellxgene_?

docs/getting-started.md

@@ -56,6 +56,12 @@ The `launch` command assumes that the data is stored in the `.h5ad` format from
 
 The `prepare` command is included to help you format your data. It uses `scanpy` under the hood. This is especially useful if you are starting with raw unanalyzed data and are unfamiliar with `scanpy`.
 
+To install cellxgene prepare alongside cellxgene launch
+
+```
+pip install cellxgene[prepare]
+```
+
 To prepare from an existing `.h5ad` file use
 
 ```