Add documentation for frequency display in Sampler widget (sugarlabs#4622)

* Add documentation for frequency display in Sampler widget

* Update documentation to use A notes as examples

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Co-authored-by: Anvita Prasad <cs23b1059.iiitdm.ac.in>

Author: AnvitaPrasad

guide/README.md

@@ -2347,6 +2347,8 @@ You can import sound samples (.WAV files) and use them with the *Set
 Instrument" block. The *Sampler* widget lets you set the center pitch
 of your sample so that it can be tuned.
 
+The pitch selector displays both the note name (such as A4) and its corresponding frequency in Hertz (Hz). This helps you understand the mathematical relationship between musical notes and sound frequencies - each octave represents a doubling of frequency (e.g., A4 is 440 Hz while A5 is 880 Hz).
+
 ### How to import sound samples ?
 By clicking the upload samples icon or by perfoming a drag and drop to sample canvas.