Add sdcard to wiki (#199)

Author: shakna-israel

wiki/sdcard.md

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+# sdcard
+
+[sdcard](https://github.com/echo-lalia/MicroHydra/blob/main/src/lib/sdcard/mhsdcard.py) provides an interface to mount and unmount the SD Card device.
+
+At its core, the module is a wrapper around the same interface that MicroPython uses.
+
+It exposes a singular class, SDCard.
+
+## constructor:
+
+`sdcard.SDCard()`
+
+> Create the class necessary for mounting the device.
+
+> Args: None.
+
+## mount:
+
+`SDCard.mount()`
+
+> Mounts the available sd card device at /sd in the filesystem.
+
+> This method always returns `None`.
+
+> If the sd card is already mounted, this method does nothing.
+
+> Additionally, if an error is encountered, a message may be sent to `stdout`.
+
+## deinit:
+
+`SDCard.deinit()`
+
+> Unmounts the mounted sd card device.
+
+> Attempting to unmount a mounted device, may cause a system error. See [MicroPython's vfs.umount](https://docs.micropython.org/en/latest/library/vfs.html#vfs.umount) for details.