Update Readmes to use python -m pip install khoj-assistant

Makes it easier to tell pip associated with which python is being
used. Easier to debug when users have different versions of python
installed (e.g 3.10 and 3.11)

src/interface/obsidian/README.md

@@ -62,9 +62,16 @@ https://user-images.githubusercontent.com/6413477/210486007-36ee3407-e6aa-4185-8
 
 ### 1. Setup Backend
 Open terminal/cmd and run below command to install and start the khoj backend
-```shell
-pip install khoj-assistant && khoj --no-gui
-```
+- On Linux/MacOS
+  ```shell
+  python -m pip install khoj-assistant && khoj --no-gui
+  ```
+
+- On Windows
+  ```shell
+  py -m pip install khoj-assistant && khoj --no-gui
+  ```
+
 ### 2. Setup Plugin
   1. Open [Khoj](https://obsidian.md/plugins?id=khoj) from the *Community plugins* tab in Obsidian settings panel
   2. Click *Install*, then *Enable* on the Khoj plugin page in Obsidian