Add troubleshooting information

Makefile

@@ -8,6 +8,7 @@
 .PHONY: build
 
 build:
+	rm -rf __pycache__ dist build
 	pyinstaller --name="qt-map-py" --windowed main.py --add-data "./assets:assets"
 
 

README.md

@@ -22,3 +22,41 @@ Run it:
 ./dist/qt-map-py/qt-map-py 33.66195 -95.55362 # start centered at given lat / lon
 ./dist/qt-map-py/qt-map-py 33.66195 -95.55362 --die # start centered at given lat / lon and close the window once the location is selected (otherwise each location is printed in a new line to stdout)
 ```
+
+## Troubleshooting
+
+If the app doesn't start, it might mean it's been compiled using different glibc version. Try rebuilding the app.
+
+If the app cannot be rebuilt, and you get this error during build:
+
+```
+Traceback (most recent call last):
+  File "/usr/bin/pyinstaller", line 33, in <module>
+    sys.exit(load_entry_point('pyinstaller==4.2', 'console_scripts', 'pyinstaller')())
+  File "/usr/lib/python3.9/site-packages/PyInstaller/__main__.py", line 114, in run
+    run_build(pyi_config, spec_file, **vars(args))
+  File "/usr/lib/python3.9/site-packages/PyInstaller/__main__.py", line 65, in run_build
+    PyInstaller.building.build_main.main(pyi_config, spec_file, **kwargs)
+  File "/usr/lib/python3.9/site-packages/PyInstaller/building/build_main.py", line 725, in main
+    build(specfile, kw.get('distpath'), kw.get('workpath'), kw.get('clean_build'))
+  File "/usr/lib/python3.9/site-packages/PyInstaller/building/build_main.py", line 672, in build
+    exec(code, spec_namespace)
+  File "/home/kuba/projects/personal/qt-map-py/qt-map-py.spec", line 6, in <module>
+    a = Analysis(['main.py'],
+  File "/usr/lib/python3.9/site-packages/PyInstaller/building/build_main.py", line 242, in __init__
+    self.__postinit__()
+  File "/usr/lib/python3.9/site-packages/PyInstaller/building/datastruct.py", line 160, in __postinit__
+    self.assemble()
+  File "/usr/lib/python3.9/site-packages/PyInstaller/building/build_main.py", line 438, in assemble
+    ctypes_binaries = scan_code_for_ctypes(co)
+  File "/usr/lib/python3.9/site-packages/PyInstaller/depend/utils.py", line 145, in scan_code_for_ctypes
+    binaries = _resolveCtypesImports(binaries)
+  File "/usr/lib/python3.9/site-packages/PyInstaller/depend/utils.py", line 319, in _resolveCtypesImports
+    load_ldconfig_cache()
+  File "/usr/lib/python3.9/site-packages/PyInstaller/depend/utils.py", line 402, in load_ldconfig_cache
+    path = m.groups()[-1]
+AttributeError: 'NoneType' object has no attribute 'groups'
+```
+
+You may have to rebuild `pyinstaller`. Go to Add/Remove Software, find
+`pyinstaller`, click on it and choose "build".