add gpiod lib prebuilt binaries for linux

linux/lib/README.md

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+# linux/lib/gpiod
+
+This is a nasty hack because the current ubuntu has an old version of libgpiod and I don't want to make others have to build that lib from source.
+Once ubuntu 21.04 is out I think this problem will be solved.
+
+-@geeksville

linux/lib/libgpiod.la

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+# libgpiod.la - a libtool library file
+# Generated by libtool (GNU libtool) 2.4.6 Debian-2.4.6-14
+#
+# Please DO NOT delete this file!
+# It is necessary for linking the library.
+
+# The name that we can dlopen(3).
+dlname='libgpiod.so.2'
+
+# Names of this library.
+library_names='libgpiod.so.2.2.1 libgpiod.so.2 libgpiod.so'
+
+# The name of the static archive.
+old_library='libgpiod.a'
+
+# Linker flags that cannot go in dependency_libs.
+inherited_linker_flags=''
+
+# Libraries that this one depends upon.
+dependency_libs=''
+
+# Names of additional weak libraries provided by this library
+weak_library_names=''
+
+# Version information for libgpiod.
+current=4
+age=2
+revision=1
+
+# Is this an already installed library?
+installed=yes
+
+# Should we warn about portability when linking against -modules?
+shouldnotlink=no
+
+# Files to dlopen/dlpreopen
+dlopen=''
+dlpreopen=''
+
+# Directory that this library needs to be installed in:
+libdir='/usr/local/lib'