How to install in custom prefix location and how to refer to capnp from a non-package location

Hi, I am trying to build and run rr on a machine where I lack root access. I am trying to follow the instructions given here.

First, I installed Cap'n Proto using the instructions using the desired prefix directory (which will be the same location for rr as well). However, rr doesn't pick it up when running cmake ../rr:

-- Checking for module 'capnp'
--   Package 'capnp', required by 'virtual:world', not found
CMake Error at /usr/share/cmake/Modules/FindPkgConfig.cmake:418 (message):
  A required package was not found
Call Stack (most recent call first):
  /usr/share/cmake/Modules/FindPkgConfig.cmake:585 (_pkg_check_modules_internal)
  CMakeLists.txt:189 (pkg_check_modules)


-- Configuring incomplete, errors occurred!

As a second question, I do not know how to tell rr the desired installation prefix where I'd like to install it. In a standard GNU autoconf setup, this would be done using the --prefix parameter, but I'm not familiar enough with CMake to know the equivalent switch here.

The rr installation instructions appear to cover only the case of an installation in a standard, usually root-owned directory (e.g. /usr/local/bin).

If rr does not support installations by non-privileged users, please state so in the documentation. I've checked the System Requirements. Thank you.

Review the linked Building-And-Installing instructions and CMakeLists.txt around line 189, where pkg-config checks for Cap'n Proto. Document how to build with a non-package Cap'n Proto prefix and choose a non-privileged rr installation prefix; the instructions are done when both commands are clear for users without root access.