Fix minor typos in README files

Author: molinav

data/basemap_data/README.md

@@ -8,7 +8,7 @@ required by [`basemap`] to work.
 
 ## Installation
 
-The package is available in PyPI and can be installed with [`pip`]:
+The package is available on PyPI and can be installed with [`pip`]:
 ```python
 python -m pip install basemap-data
 ```

data/basemap_data_hires/README.md

@@ -8,7 +8,7 @@ data assets.
 
 ## Installation
 
-The package is available in PyPI and can be installed with [`pip`]:
+The package is available on PyPI and can be installed with [`pip`]:
 ```python
 python -m pip install basemap-data-hires
 ```