Ubuntu Installation Issue

Unable to install on Ubuntu 20.04 following the directions from the cmake file here:

https://github.com/yhirose/cpp-httplib/blob/master/CMakeLists.txt#L26

Here's the output:



```

ryan@drogon:~/Desktop/cpp-httplib$ mkdir build

ryan@drogon:~/Desktop/cpp-httplib$ cd build

ryan@drogon:~/Desktop/cpp-httplib/build$ cmake -DCMAKE_BUILD_TYPE=Release ..

-- The CXX compiler identification is GNU 9.3.0

-- Check for working CXX compiler: /usr/bin/c++

-- Check for working CXX compiler: /usr/bin/c++ -- works

-- Detecting CXX compiler ABI info

-- Detecting CXX compiler ABI info - done

-- Detecting CXX compile features

-- Detecting CXX compile features - done

-- Looking for C++ include pthread.h

-- Looking for C++ include pthread.h - found

-- Performing Test CMAKE_HAVE_LIBC_PTHREAD

-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Failed

-- Looking for pthread_create in pthreads

-- Looking for pthread_create in pthreads - not found

-- Looking for pthread_create in pthread

-- Looking for pthread_create in pthread - found

-- Found Threads: TRUE  

CMake Error at /usr/share/cmake-3.16/Modules/FindPackageHandleStandardArgs.cmake:226 (message):

  No REQUIRED_VARS specified for FIND_PACKAGE_HANDLE_STANDARD_ARGS()

Call Stack (most recent call first):

  cmake/FindBrotli.cmake:176 (find_package_handle_standard_args)

  CMakeLists.txt:146 (find_package)





-- Configuring incomplete, errors occurred!

See also "/home/ryan/Desktop/cpp-httplib/build/CMakeFiles/CMakeOutput.log".

See also "/home/ryan/Desktop/cpp-httplib/build/CMakeFiles/CMakeError.log".

```





I have brotli installed via apt:



```

ryan@drogon:~/Desktop/cpp-httplib/build$ apt list | grep brotli



WARNING: apt does not have a stable CLI interface. Use with caution in scripts.



brotli/focal,now 1.0.7-6build1 amd64 [installed]

...

```

[]