Add patch_url kwarg for signing hrefs and objects (#31)

This seems like potentially a better approach than just signing
everything but it would be great to get a second opinion

closes #29

Author: jsignell

.github/workflows/tests.yml

@@ -46,4 +46,4 @@ jobs:
 
       - name: run tests
         id: status
-        run: pytest -v --cov xpystac --cov-report term-missing .
+        run: pytest -v --cov xpystac --cov-report term-missing --block-network .

README.md

@@ -47,7 +47,7 @@ Read from a reference file:
 collection = catalog.get_collection("nasa-nex-gddp-cmip6")
 asset = collection.assets["ACCESS-CM2.historical"]
 
-xr.open_dataset(asset)
+xr.open_dataset(asset, patch_url=planetary_computer.sign)
 ```
 ref: https://planetarycomputer.microsoft.com/dataset/nasa-nex-gddp-cmip6#Example-Notebook
 
@@ -58,14 +58,14 @@ Read from a zarr file:
 collection = catalog.get_collection("daymet-daily-hi")
 asset = collection.assets["zarr-abfs"]
 
-xr.open_dataset(asset)
+xr.open_dataset(asset, patch_url=planetary_computer.sign)
 ```
 ref: https://planetarycomputer.microsoft.com/docs/quickstarts/reading-zarr-data/
 
 ## Install
 
 ```bash
-pip install xpystac
+pip install git+https://github.com/stac-utils/xpystac
 ```
 
 ## How it works

environment.yaml

@@ -22,3 +22,4 @@ dependencies:
   # testing
   - pytest
   - pytest-cov
+  - pytest-recording