Fix typo in fbt.md (flipperdevices#2539)

availabe -> available

Co-authored-by: あく <[email protected]>

documentation/fbt.md

@@ -72,7 +72,7 @@ To run cleanup (think of `make clean`) for specified targets, add the `-c` optio
 - `get_stlink` - output serial numbers for attached STLink probes. Used for specifying an adapter with `OPENOCD_ADAPTER_SERIAL=...`.
 - `lint`, `format` - run clang-format on the C source code to check and reformat it according to the `.clang-format` specs.
 - `lint_py`, `format_py` - run [black](https://black.readthedocs.io/en/stable/index.html) on the Python source code, build system files & application manifests.
-- `firmware_pvs` - generate a PVS Studio report for the firmware. Requires PVS Studio to be availabe on your system's `PATH`.
+- `firmware_pvs` - generate a PVS Studio report for the firmware. Requires PVS Studio to be available on your system's `PATH`.
 - `cli` - start a Flipper CLI session over USB.
 
 ### Firmware targets