Add ChipNorm_SHT21 library

[chipnorm]

No description provided.

[github-actions]

Arduino Lint has suggestions for possible improvements to https://github.com/chipnorm/SHT21:

Linting library in SHT21
WARNING: Unable to load the library.properties url field: 404 Not Found                                        
         See: https://arduino.github.io/arduino-cli/latest/library-specification/#libraryproperties-file-format
         (Rule LP042)                                                                                          
WARNING: Sketch(es) found outside examples and extras folders:                                    
           SHT21/example/ESP32_GY21_SHT21_ChipNorm                                                
         See: https://arduino.github.io/arduino-cli/latest/library-specification/#library-examples
         (Rule LD003)                                                                             
WARNING: Potentially misspelled examples folder name found: SHT21/example                         
         See: https://arduino.github.io/arduino-cli/latest/library-specification/#library-examples
         (Rule LD005)                                                                             

Linter results for project: 0 ERRORS, 3 WARNINGS

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Linting sketch in SHT21/example/ESP32_GY21_SHT21_ChipNorm

Linter results for project: no errors or warnings

-------------------

Linter results for projects: 0 ERRORS, 3 WARNINGS

[github-actions]

Your submission has now been accepted! Thanks for your contribution to the Arduino Library Manager index.

The library(s) will be available for installation via Library Manager within a day's time.

You can check the logs from the Library Manager indexer for your library(s) here:
http://downloads.arduino.cc/libraries/logs/github.com/chipnorm/SHT21/