[FCE-980] Fix link to License file (#273)

## Description

This PR change license file extension, as without it I can't generate
correct HTML output.

## Motivation and Context

When generating documentation, I get errors that links are broken and
HTML tag cannot be parsed


## How has this been tested?

No testing needed, as this is only README update

## Types of changes

- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to
      not work as expected)

## Checklist:

- [ ] My code follows the code style of this project.
- [ ] My change requires a change to the documentation.
- [ ] I have updated the documentation accordingly.

## Screenshots (if appropriate)

Co-authored-by: Miłosz Filimowski <[email protected]>

README.md

@@ -1,4 +1,4 @@
-<img src="./.github/images/fishjam-card.png" width="100%">
+<img src="./.github/images/fishjam-card.png" width="100%" />
 
 # Fishjam Mobile Client
 

packages/react-native-client/README.md

@@ -1,4 +1,4 @@
-<img src="../../.github/images/fishjam-card.png" width="100%">
+<img src="../../.github/images/fishjam-card.png" width="100%" />
 
 # Fishjam React Native client
 
@@ -20,7 +20,7 @@ There is simple example app, that allows you to test our service. To run it loca
 
 ## License
 
-Licensed under the [Apache License, Version 2.0](LICENSE)
+Licensed under the [Apache License, Version 2.0](./LICENSE.txt)
 
 ## Fishjam is created by Software Mansion