Sergei Trofimovich
33fa5f3cd9
doc/manual/local.mk: fix 'make install DESTDIR=...'
Install failure is observed when we try to install
into inplace location as non-root:
```
$ LANG=C make install DESTDIR=$PWD/__i__ V=1
RUST_LOG=warn mdbook build doc/manual -d /usr/share/doc/nix/manual
2021-08-28 13:29:58 [ERROR] (mdbook::utils): Error: Rendering failed
2021-08-28 13:29:58 [ERROR] (mdbook::utils): Caused By: Unexpected error when constructing destination path
2021-08-28 13:29:58 [ERROR] (mdbook::utils): Caused By: Permission denied (os error 13)
make: *** [doc/manual/local.mk:98: /usr/share/doc/nix/manual/index.html] Error 101
```
The change is to prefix paths with `$(DESTDIR)`.