docs: added change logs for 2.0.19 (fossasia#1962)

Author: CloudyPadmal

fastlane/metadata/android/en-US/changelogs/20.txt

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+# Release notes for PSLab Android app version 2.0.19
+
+## :rocket: Features and Enhancements
+
+- fix: osc main screen ui changes
+- fix: Wave generator UI changes
+- feat: bluetooth wifi connection option moved to Connect device menu
+- feat: new FAQs added
+- feat: new Wave Generator UI
+- fix: Actionbar added to Oscilloscope and Robotic Arm
+- fix: scroll added to create config layout
+- feat: add Httphandler class
+
+## :bug: Bug Fixes
+
+- fix: action bar added to logic analyzer
+- fix: Wave generator active even without pressing view button
+- fix: side navbar rearranged
+- fix: multimeter action bar fixed
+
+## :page_facing_up: Documentation
+
+- docs: readme images changed
+
+## :wrench: Maintenance
+
+- chore: upgrade app version