added simple readmes to examples`

Author: gigapod

examples/all_allocator/README.md

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+## all_allocator
+
+This example detects the PSRAM available on the board, and adds it as well as the built in SRAM based heap to an allocator to provide an unified access to available memory. The allocator manages the *allocation* of the PSRAM and heap SRAM via a single API. The example also ```wraps``` the built in ```malloc``` and ```free``` suite of commands to integrate with existing examples and uses.
+
+A "Two-Level Segregated Fit" (flsf) allocator is used from [here](https://github.com/espressif/tlsf).

examples/has_psram/README.md

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+## has_psram
+
+One of the more simple examples, this example shows how to detect if PSRAM is on the rp2350 board, and the size of the PSRAM available. It also walks through the available PSRAM, manually setting and verifying values.

examples/psram_allocator/README.md

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+## psram_allocator
+
+This example detects the PSRAM available on the board, and adds it to an allocator, which manages the *allocation* of the PSRAM. PSRAM is accessed (allocated) using a provided API, which mimics the standard malloc/free functionality.  
+
+A "Two-Level Segregated Fit" (flsf) allocator is used from [here](https://github.com/espressif/tlsf).

examples/set_qflash/README.md

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+## test_qflash
+
+This is a simple example that is used to verify the Quad SPI bit is set in the flash IC used on the attached board. It doesn't require the use of the ```sparkfun_pico``` library, but is helpful during board development and fits with the goals of this repository.